Abducent nerve (CN VI): The sixth cranial nerve. Innervates the lateral rectus muscle, which abducts the eye, or rotates it outward. See the Cranial Nerve Table.

Ablation: The removal or destruction of tissue.

Acetylcholine: A neurotransmitter that is important for memory and muscle movement.

Acoustic neuroma: A tumor which results from the growth of Schwann cells surrounding the acoustic nerve, CN VIII.

Activation Synthesis Hypothesis: a theory suggesting that dreams are a result of random activation of the cortex.

Acupuncture: A technique used principally for pain management and anaesthesia. An acupuncture practioner uses fine needles to manipulate the body's endogenous pain repression mechanisms.

Adenosine: A nucleotide consisting of adenine linked to the sugar ribose.

Adrenaline: Also called epinepherine, a neurotransmitter that is important for regulating heart rate.

Adrenocorticotrophin (ACTH): A peptide hormone released by the pituitary that stimulates the production of steroid hormones in the adrenal gland.

Agoraphobia: An extreme fear of open spaces. An anxiety disorder characterized by extreme fear of leaving home due to increased likelihood of having a panic attack outdoors.

Agnosia: Literally "not knowing," agnosia is the condition of not recognizing sensory stimuli. For example, someone with visual agnosia would have no trouble seeing an object, but lacks the ability to understand the image.

Allocentric: A spatial system referencing objects external to the body, as opposed to an egocentric system.

Alpha Motor Neuron: Large neurons in the ventral horn of the spine which innervate the force-producing skeletal muscle fibers.

Alphabetic principal: awareness that letters can represent the sounds of words.

Alzheimer's disease: A degenerative, age-related form of dementia.

Amacrine cell: A type of neuron in the retina which helps to shape the receptive fields of retinal bipolar cells through inhibitory influence.

Amblyopia: A condition resulting from strabismus in one eye. Visual acuity in the effected eye is decreased due to weakened connections with visual cortex, resulting in a loss of focus in an otherwise healthy eye.

Amnesia: A cognitive disorder involving memory loss, typically as a result of a traumatic injury or a degenerative brain condition.

Amygdala: A part of the basal ganglia named for its almond shape. The amygdala is thought to be involved with emotion and memory formation.

Analgesic

Aneurysm: The swelling or rupture of an artery, resulting from increased arterial pressure due to a clot or obstruction.

Angular Gyrus: A section of the left temporal lobe involved in language processing; it connects the occipital cortex with Wernicke's Area.

Anoxia: A lack of adequate oxygen, typically resulting in tissue injury and cell death; oxygen starvation.

Anterior cingulate gyrus: An area of the brain associated with motor control, pain perception, cognitive function and emotional arousal. A component of the limbic system.

Anthropometry: The comparative study of human body measurements.

Aphasia: Partial or total loss of the ability to express ideas or comprehend spoken or written language, resulting from damage to the brain caused by injury or disease.

Aqueous humor: Literally "water-like fluid," the aqueous humor fills the space between the cornea and the iris in the eye.

Asperger's Syndrome: A diagnosis given to high-functioning individuals with autism who have normal or above-average IQs and no clinically significant delays in language acquisition, age-appropriate self-help skills, or cognitive development.

Aspiration: Audible breath that accompanies some sounds when speaking.

Astigmatism: Aberrations in the surface of the cornea occurring during development. The resulting uneven corneal surface causes difficulties in focusing.

Astrocytes: Star-shaped glia cells that help form the blood-brain barrier and provide a support system for central nervous system axons.

Ataxic palsy: A type of motor control disorder characterized by uncontrolled muscle movement and loss of balance.

Athetoid palsy: A type of motor control disorder characterized by repeated involuntary slow, writhing movements.

Attention Deficit Disorder (ADD): A syndrome characterized by short attention span and poor impulse control.

Attention Deficit Hyperactivity Disorder (ADHD): A syndrome generally characterized by inattention, distractibility, impulsivity, and hyperactivity.

Atrophy: A wasting away of part of the body.

Atypical depression: a type of depressive illness whose symptoms may include oversleeping, overeating, mood brightening in response to positive events, and extreme sensitivity to rejection or adversity.

Auditory feedback: The process by which humans learn to speak utilizing hearing and vocalization. In auditory feedback sounds heard are repeatedly mimicked and fine-tuned until they can be perfectly reproduced.

Auditory Nerve: The eighth cranial nerve, also called the acoustic nerve, or the vestibulocochlear nerve. Bundled nerve fibers extending from the cochlea of the ear to the brain. The bundle contains two branches: the cochlear nerve, which transmits sound information, and the vestibular nerve, which delivers information about balance. See the Cranial Nerve Table.

Autism: The three core features of this pervasive developmental disorder which appears early in life are: qualitative impairments in social interactions; repetitive, restricted and stereotyped behavior patterns; and impairments in communication. Autistic Savant: The name given to an individual with autism who also possesses extraordinary skills not generally exhibited by others. Autistic spectrum: Term used to describe a range of symptoms generally associated with autism.

Autobiographical Self: a term used by Antonio Damasio to represent our notion of self in terms of traits we consider part of our identity. It depends on systematic memories of facts and experiences that we consider the essence of who we are.

Autonomic Nervous System: Also called the visceral nervous system. Located outside the brain and spinal cord. Obtains sensory information from internal organs and provides output to them.

Autoreceptor: A receptor that resides near the presynaptic terminals; when activated, it usually prevents further transmitter release. Axon: An extension of a neural cell that transports information to and from the cell body, usually by an electrical impulse.

Balanced bilingualism: Equal fluency in both languages across contexts.

Basal Forebrain: the bottom surface of the forebrain, a region of the brain associated with emotional decision-making.

Basal Ganglia: A series of subcortical structures in the center of the brain that are principally responsible for motor tasks.

Basilar Membrane: A membrane inside the cochlea on which the hair cells rest. It is between the scala tympani and the scala media.

Behaviorism: School of psychological thought limited to the study of observable and quantifiable aspects of behavior.

Benign Paroxysmal Positional Vertigo: Disorder which causes dizziness, nausea, and imbalance. Results from the movement of calcium carbonate crystals in the ear.

Benzodiazepines: Drugs such as valium and librium, most frequently prescribed for anxiety.

Binaural: Relating to both ears. Alfred Binet: (1857-1911) French psychologist credited with creating the first psychometric intelligence scale (1905).

Binet-Simon Scale: Testing device created by Alfred Binet and Theodore Simon in France in 1905; the precursor to the modern intelligence test.

Binocularity of vision: Vision with two eyes (or sensors) allowing the apprehension of stereoscopic depth.

Bipolar cell: A type of neuron in the retina which exhibits either on-center or off-center response properties. Bipolar cells are thought to be responsible for contrast and edge detection.

Bipolar disorder: manic-depressive illness, symptoms of which include alternating periods of depressive moodiness and high-energy activity.

Blastula: An early stage in animal embryology; in many species, a hollow sphere of cells surrounding a central cavity.

Blind spot: A spot in the visual field of each eye where the eye cannot see. The blind spot corresponds to the point in the retina where the optic nerve exits the eye, and which is devoid of photoreceptors.

Bone conduction: Conduction of sound through bones directly to the cochlea, which is housed in the mastoid, a part of the temporal bone.

Brain Hemisphere Laterality: The differences in the abilities of the right and left hemispheres of the brain.

Brainstem: The major route by which the forebrain communicates with the spinal cord and peripheral nerves. The brainstem controls, among other things, respiration and regulation of heart rhythms.

Broca's Area: The central region for the production of speech. Located in the frontal lobe, typically in the left hemisphere.

Paul Broca: (1824-1880) French surgeon and anthropologist who first located a center of motor and speech in the brain, a region now known as Brocas Area.

Brodmann Area 17: An area of cortex in the occipital lobe. Also called the V1, or primary visual cortex, because it receives the earliest information from the eyes by way of the thalamus. Also called striate cortex because in cross section, it has a distinct band of white myelin within the cell layer.

Capillaries: the smallest of blood vessels, often just big enough to allow red blood cells to move in single file. Capillary beds are the site of nutrient and waste exchange for most tissues.

Capsaicin: The substance found in the white "ribs" of chili peppers which provide the peppers with their characteristic hot flavor.

Carbohydrate: The nutritional group consisting of simple and complex sugars–pasta, sweets, and many fruits and vegetables fall into this category.

CAT (Computerized Axial Tomography) Scan: A computer-mediated x-ray image depicting a cross-section of the body.

Cataract: A clouding of the eye’s lens, typically a result of the aging process. Cataract causes dim or unfocused vision.

Central executive: A component of the working memory models associated with coordinating cognitive functions.

Central Gray: Region of the midbrain that controls freezing during times of fear.

Cerebral Aqueduct: A channel for cerebrospinal fluid running near the brainstem. The cerebral aqueduct connects the third and fourth ventricles, which are fluid reservoirs within the brain.

Cerebral palsy: A developmental disorder characterized by motor control difficulties; cerebral palsy results from perinatal damage to brain tissue.

Central Nervous System (CNS): The "Central Station" to which the peripheral and visceral (autonomic) systems send their sensory information. The CNS takes that sensory information and responds to the peripheral and visceral systems with motor instructions. The two main structures of the CNS are the brain and the spinal cord.

Central Sulcus: A deep groove within the convolutions of the cerebral cortex that runs from the midline down the side of the brain and delineates the frontal lobe from the rest of the cortex.

Cephalometry: The science of measuring the heads of living humans.

Cerebellum: A large structure located high inside the hindbrain. Connected to the pons, medulla, spinal cord and thalamus. Helps control movement and some aspects of motor learning.

Cerebral Cortex: The outer, highly convoluted layer of the cerebral hemispheres. Responsible for perception, emotion, thought and planning.

Cerebral Hemispheres: The halves of the brain, each with its own specific functions. The left hemisphere is typically associated with speech, writing, language and calculation, and the right hemisphere is typically associated with spatial perception, visual recognition, and aspects of music perception and production.

Cerebrospinal fluid: a fluid that surrounds the brain and spinal cord, providing nutrients to nerve tissue, removing cellular waste products, and cushioning the brain.

Cervical Level (of the spine): Portion of the spine that lies closest to the brainstem, there are 7 cervical vertebrae.

Childhood Disintegrative Disorder: A pervasive developmental disorder related to autism characterized by regression to severe disability following development that is initially normal.

Cholesteatoma: Benign tumor in the middle ear resulting from the overgrowth of tissue during repair of a tear in the ear drum.

Cholinergic: Uses the neurotransmitter acetylcholine.

Chopper response pattern: An activity pattern exhibited by neurons in the cochlear nucleus called "chopper units." The chopper response pattern is characterized by repeated, rhythmic bursts of action potentials separated by relatively fixed time intervals.

Chromosome: thread-like structure of the cell nucleus that contains genetic information; they occur in characteristic matched pairs for each species, humans have 23 pairs.

Chronic: Of long duration.

Cingulate Gyrus: A cortical structure, part of the limbic system, that is directly over the corpus callosum along the medial side of each hemisphere. It is involved with emotion and attention.

Circadian rhythm: From the Latin "circa" meaning "about" and "diem" meaning "day", the term refers to any event that occurs cyclically every 24 hours.

Classical Conditioning: A type of learning in which an organism comes to associate different events; also called Pavlovian conditioning or associative conditioning.

Cochlea: The inner ear. The location where the mechanical energy of sound is transduced into electrical signals that can be carried by the nervous system. The cochlea also contains the semicircular canals that are responsible for our sense of balance.

Cochlear Implant: A prosthetic, implanted, device that replaces the function of the cochlea in order to restore hearing. A microphone outside the head captures the sound and then transforms it into electrical signals which are sent to the auditory nerve directly.

Cochlear Nerve: The part of the VIIIth Cranial Nerve (auditory-vestibular or vestibulocochlear nerve) that carries information about hearing from the cochlea to the brainstem.

Cochlear Nucleus: One of the auditory nuclei in the brainstem.

Cognition: The mental processes by which knowledge or awareness is applied tor comprehension and problem-solving.

Cognitive interference: The theory that certain cognitive processes in the brain may conflict with other cognitive processes. See "Stroop Effect."

Cognitive map theory: One theory concerning how the brain represents physical spaces.

Commissurotomy: Surgery, generally for sufferers of severe epilepsy, in which the hemispheres of the brain are disconnected from one another by the severing of the corpus callosum, and occasionally the many other commissuries, or connectors.

Concussion: Changes of cerebral function caused by a direct or indirect force transmitted to the head. Symptoms include headaches, dizziness, confusion, vision impairment, nausea/vomiting or loss of consciousness.

Conditioned Stimulus (CS): In classical conditioning, an originally neutral stimulus that, after association with an unconditioned stimulus, comes to trigger a conditioned response.

Conditioned Response (CR): In classical conditioning, the learned response to a conditioned stimulus.

Conductive Hearing Loss: Hearing loss which disrupts the conduction of sound to the auditory nerve-involves pathology of the outer or middle ear.

Cone cell: A type of photoreceptor in the retina. Cone cells are responsible for high-acuity color and black and white vision.

Consolidation: A stage of memory formation during which long-term memories are created.

Context Conditioning: A type of learning in which an organism associates its surroundings with a particular stimulus.

Contralateral: Related to the opposite side, as when functions on the right side of the body are controlled by the left side of the brain.

Cornea: A thin, clear layer of tissue which protects the front of the eye. The cornea provides the eye with most of its optical focusing power.

Corneal blink reflex: A normal reflex blinking induced by touching the cornea lightly.

Corpus Callosum: A large bundle of nerve fibers that connects the left and right cerebral hemispheres.

Corticospinal Tract: Direct pathway from the cortex to the spine, involved in voluntary motor control.

Cortisol: A steroid hormone produced by the adrenal cortex.

Craniometry: The science of measuring skull volume.

Cortical Plasticity: The ability for connections between neurons to be modified within the cortex.

Critical period, or sensitive period: The period of development during which an individual can permanently acquire certain behaviors or attributes; during this period, the individual is sensitive to the experiences or environmental influences that foster these capacities.

Cranial nerves: A series of twelve large nerve bundles that control a variety of functions in the head and neck. See the Cranial Nerve Table.

Cytokines: Non-antibody proteins released by certain cells (maternal and fetal during pregnancy) that may have stimulating, repressive, or even toxic effects on other cells and tissues.

DNA: see Deoxyribonucleic Acid Declarative memory: Memory for semantic information that can be consciously (and verbally) recalled.

Decussation: A crossing over of nerve fiber tracts from one side of the body's midline to the other. Decussations typically result in the right hemisphere of the brain controlling the left side of the body, and the left hemisphere controlling the right side of the body.

Demyelination Disease: A disease of the nervous system in which myelin is damaged. Must be differentiated from dysmyelination disease. In the former, normal myelin is damaged; in the latter, the myelin is probably abnormal in the first place.

Dendrite: A branching extension from the neuron cell body that receives information from other neurons.

Dendritic Branching: The process in which the neuron is stimulated to produce new dendrites, which increase the neuron's communicative ability.

Dendritic sprouting: A process in which the branches of a neuron that receive information (dendrites) multiply to increase the communicative power of the neuron.

Deoxyribonucleic Acid (DNA): A long, thread-like molecule contained in the nucleus of cells that encodes the genetic information of an organism. DNA is a remarkable molecule because it can self-replicate. Half of a child's DNA contains genetic information from the mother, and half from the father.

Rene Descartes: (1596-1650) French philosopher who founded analytic geometry; often remembered for his ideas about a split between mind and body. Diathesis-Stress Model: A model for all types of illness that suggests one can have a certain predisposition for a particular disorder that may or may not manifest itself, depending on the environmental conditions.

Diencephalon: That part of the forebrain which gives rise to the thalamus, hypothalamus, infundibulum (pituitary stalk), and part of the pituitary gland.

Discrimination: In classical conditioning, the organism will only respond to cues that are very similar to the conditioned stimulus.

Diurnal: An organism that is generally awake during daytime and asleep during night.

Dopamine: A neuromodulator acting principally through structures of the basal ganglia. Dopamine is associated with reward pathways, and low levels of dopamine are characteristic of Parkinson's disease.

Dorsal: In humans, closer to the back of the body.

Dorsolateral prefrontal cortex: An area on the lateral aspect of the brain near the front that is associated with executive function, decision making, and working memory.

Drosophila: Genus name of the common fruit fly; extremely useful in the study of genetics.

Dyscalculia: A "number blindness" that is an impairment of the ability to recognize or manipulate numbers.

Dyskinesia: A condition characterized by abnormal involuntary movements.

Dyslexia: A reading impairment affecting the ability to identify, sound out, or understand written letters and words that is not attributable to sensory deficit or cognitive impairment.

Dystonia: Sustained muscle contractions causing abnormal motor control. For example, co-contraction of flexors and extensors (opposing muscle groups) resulting in the lack of motor control of a limb.

Eardrum: Also referred to as the tympanic membrane. The membrane separating the external ear canal from the middle ear.

Ectoderm: The outermost of the three embryonic tissue layers first delineated during gastrulation; gives rise to the skin, sense organs and nervous system.

Ectopic cells: Cells that have migrated incorrectly and cannot develop into functioning cells as a result Ð a minor brain malformation.

Edema: Swelling caused by the accumulation of an excessive amount of fluid in cells, tissues or cavities.

Thomas Edison: (1847-1931) US inventor responsible for the creation of the incandescent electric light (1879) and the phonograph (1877).

Egocentric: A spatial system referencing the self, as opposed to an allocentric system.

Albert Einstein: (1879-1955) German-born (Swiss/U.S. citizen) physicist. Discovered Special Theory of Relativity (1905); won Nobel Prize in Physics in 1921.

Electroencephalogram (EEG): A record of the summed activity of cortical cells picked up by wires placed on the skull.

Embolism: Obstruction of a vessel by a transported clot or mass, called an embolus.

Embryo: A young organism while it is still contained within a protective structure such as a seed, egg or uterus.

Encephalopathy: a disease or injury of the brain

Endocrine system: System of glands that release hormones into the circulatory system; regulated by the hypothalamus.

Endoderm: The innermost of the three embryonic tissue later first delineated during gastrulation; gives rise to the digestive and respiratory systems.

Endolymph: Fluid in the scala media.

Endorphins: molecules in the body that are part of the pain signaling pathway; endorphins suppress pain sensation.

Enlightenment: Eighteenth century philosophy of reason and individualism.

Entorhinal cortex: evolutionary older cortex in the temporal lobes, located near the hippocampus; may be involved in learning and memory.

Enzyme: Protein molecule that catalyzes reactions between other substances.

Epidermis: In plants and animals, the outermost cell layers.

Epilepsy: A neurological disorder caused by uncontrolled electrical activity that spreads throughout the brain, causing seizures that can last from seconds to several minutes.

Equilibrium: Sense of balance.

Eugenics: The science of improving hereditary qualities (of a race or breed) through mating control.

Eustachian Tube: Thin tube which connects the middle ear to the back of the throat and acts to drain the ear and to equalize the air pressure across the ear drum.

Executive processes: Cognitive tasks related to decision-making, associated with the frontal lobe of the brain.

External auditory meatus: The ear canal.

Extrastriate: Visual areas in the cerebral cortex which are "downstream" of primary visual cortex. Extrastriate areas are associated with higher order features of vision, such as face recognition and spatial awareness

Facial nerve (CN VII): The seventh cranial nerve, responsible for facial movements, taste, salivation, and lacrimation. See the Cranial Nerve Table.

Finger agnosia: Confusion in identifying individual fingers, literally "not knowing" one's own fingers.

Focal dystonia: A localized dystonia such as one affecting just the hand.

Factor Analysis: Analytical process of converting two or more measurements into linear combinations of usually independent variables.

Forebrain: (See Prosencephalon) Fovea: A region near the center of the retina which has a very high density of photoreceptors. The fovea is the part of the retina used to read or to analyze detailed stimuli.

Free radicals: unusually charged ions that are highly chemically reactive. The free radical form of oxygen (O-) is responsible for a type of damage to neurons called "oxidative injury."

Frontal cortex: An area of the brain associated with higher cognitive functions including planning and motor control.

Frontal lobe: One of the four divisions of each hemisphere of the cerebral cortex that include the parietal, temporal, occipital. The site of emotions, personality, cognitive and motor functions.

Fusiform gyrus : Holds the functional regions responsible for color, identification of a face and recognition of facial expression. Damage to any of these areas leads to a deficit specific for that mode of visual function.

Functional Magnetic Resonance Imaging (fMRI): A technique for imaging brain activity using magnets. fMRI is able to detect brain activity by taking advantage of the fact that deoxyhemoglobin has a different magnetic profile than oxyhemoglobin. Deoxyhemoglobin is concentrated in areas of high cellular metabolism, which correlates to high cellular activity.

Ganglion cell: A type of neuron in the retina. These are the only retinal neurons which communicate directly with the rest of the brain. Joseph Gall: (1758-1828): German physician who founded phrenology.

Gamma Motor Neuron: Motor neurons in the spine which innervate muscle spindles.

Howard Gardner: (1943-) Harvard psychologist whose 1983 book Frames of Mind: The Theory of Multiple Intelligences revolutionized thinking about intelligence testing.

Gene: The smallest hereditary unit. A gene is a section of DNA that encodes a protein, and proteins in turn control many characteristics of an organism.

General Intelligence Factor: Psychometric measurement that suggests a global capacity for intelligence.

Generalization: In classical conditioning, the organism will repond to cues that approximate the conditioned stimulus, e.g., a tone that is very close in pitch to the CS.

Generalized Anxiety Disorder (GAD): A psychological disorder characterized by long lasting, intense worry and a pervasive sense of dread. Genome: The complete set of genes within an organism.

Genomics: The study of the structure and function of the genome within an organism.

Glial Cells: A range of cell types that act to support the neural network by providing structure and nourishment. In some cases, glia may be involved in modulating neural signals.

Globus pallidus: A nucleus of the basal ganglia that is involved in the coordination of voluntary movement.

Glottalization: the closing of the gap between the vocal folds when speaking.

Glial cells: Cells found only in the nervous system that do not conduct action potentials; they provide a support system for the neurons.

Glossopharyngeal nerve (CN IX): The ninth cranial nerve, responsible for taste and swallowing. See the Cranial Nerve Table.

Golgi Tendon Organ: Stretch receptor located in the tendon connecting muscle to bone, provides information on contractile force.

Grand mal seizure: In epilepsy, a type of seizure characterized by loss of consciousness, muscle spasms and rigidity.

Graphesthesia: Ability to recognize letters traced on the hand.

Growth cone: Located at the tip of a sprouting axon, uses chemical messages to determine the axon's correct path.

Gyri (singular, Gyrus): The outer, visible convolutions of the cerebral cortex.

Helicotrema: The channel at the tip of the cochlea where the scala vestibuli and the scala tympani are continuous. Hemisphere: Half of the brain, the right or left.

Hertz (Hz): A unit describing the frequency with which something occurs. Measured in occurrences per second.

Hindbrain: (See Rhombencephalon) Hippocampus: A cortical structure near the center of the brain which plays an important role in memory. The hippocampus is named for its seahorse-like shape in cross section.

Homeobox genes: Genes containing a special segment of DNA that seems to regulate the expression of other genes and thus controls large-scale developmental processes.

Homeostasis: Balance or equilibrium, typically between the chemical environment of the body and the external environment.

Homeothermic: Describes animals with the ability to maintain a constant body temperature that is relatively independent of environmental temperature. Also known as warm-blooded which is a bit of a misnomer because the key feature of a homeothermic animal is that it can regulate a constant body temperature, not that it has a particularly high body temperature.

Horizontal cell: A type of neuron in the retina which is responsible for shaping the receptive field of retinal bipolar cells through inhibitory influences.

Hormone: a chemical that helps regulate the body's internal environment by traveling through the blood stream and binding to cells in target tissues. Hormones control metabolism, growth, sexual rhythms, and reproduction.

Hydrocephaly: Also called "water on the brain." A condition characterized by increased intracranial pressure due to excessive acccumulation of fluid in the cerebral ventricles.

Hypertrophy: Overgrowth of the branches of a neuron. Hypoglossal nerve (CN XII): The twelfth cranial nerve, innervating the muscles of the tongue. See the Cranial Nerve Table.

Hyperopia: Also known as farsightedness, because far objects appear in focus while near objects are blurry. Hyperopia is the result of an overly short eyeball.

Hypothalamus: A brain structure providing specific functions such as regulating the activities of internal organs, monitoring information from the autonomic (peripheral) nervous system and controlling the pituitary gland.

Immediate memory: A type of very short-term memory used to maintain information "online" during an experience. Immediate memory occurs over time scales of a second and less.

Incus: One of the three middle ear bones -- the center bone.

Infantile amnesia: The term used to describe the profound lack of memories from ages 0-3 years.

Infarct: An area of tissue death caused by loss of blood flow to the tissue.

Inferior Colliculus: A cluster of cells responsive to sound. Found in the brainstem below the superior colliculus.

Inferior Parietal Lobe: A region of the parietal lobe associated with object recognition.

Infereotemporal Cortex: The lower part of the temporal lobe, an area of the brain involved in object and number recognition.

Inhibitory: Referring to a synaptic connection that decreases the electrical excitability of the postsynaptic neuron.

Inner Ear: The part of the auditory system which includes the cochlea-site of the transformation of the mechanical representation of sound to electrical signals.

Insomnia: A disorder characterized by prolonged periods with little or no sleep.

Intelligence Quotient: The product of dividing mental age by chronological age. I.Q. is a revision by German psychologist W. Stern of Alfred Binets original formula of subtracting mental age from chronological age.

Interneuron: The generic term for a cell in a local network of neurons. Interneurons typically modify the response properties of the cells that they connect to.

Inversion Effect: Difficulty in remembering faces when they are presented upside-down. Ions: small, electrically charged elemental molecules. Some important ions for neural function are sodium (Na+), potassium (K+), chlorine (Cl-), and calcium (Ca2+).

Ipsilateral: Related to the same side, as when stimuli presented to the left side of the body are detected by the left hemisphere of the brain.

Iris: A circular structure with an opening in its center and muscles that dilate or constrict the pupil in order to control the amount of light that enters the eye.

Isocortex: Literally meaning "same cortex," because it has similar structure throughout. Also known as neocortex. Located in the dorsal, or front part of the brain, the isocortex is especially large in higher primates and is responsible for sensory and motor processing as well as abstract reasoning and association.

Kinesthesis: The sense by which muscular motion, weight, position, etc., are perceived.

Kluver-Bucy Syndrome: A pattern of complex behavioral changes (e.g. tameness and hypersexuality) that is induced in several species by bilateral damage to the anterior temporal lobes.

Knockout Mouse: A mouse which has been genetically engineered to no longer express a particular gene. Scientists use these mice to determine the role of a gene by studying what happens to behavior and physiology when the gene is removed.

L-dopa (also called Levodopa): A drug used to replenish the dwindling supply of the neurotransmitter dopamine. L-dopa can cross the blood-brain barrier to be converted into dopamine by nerve cells.

Larynx: The organ of voice production, also called the "voicebox."

Lateral Hypothalamus: A nucleus within the hypothalamus that helps regulate blood pressure.

Lateralization: Result of cerebral dominance of one hemisphere or the other for a specific function as demonstrated in the opposite side of the body, as in handedness.

Lateral: Referring to a structure that is closer to the side or surface of another structure, as opposed medial. For example, the lateral part of an egg is the egg white, and the medial part is the yolk.

Lateral Connections: Synaptic connections between neighboring neurons that modify information flow through those neurons. Lateral connections tend to be inhibitory.

Lateral Fissure: A deep sulcus (groove) within the convolutions of the cerebral cortex. Delineates the temporal lobe from the rest of the cortex.

Lateral hypothalamus: a nucleus in the hypothalamus involved in functions including metabolic regulation.

Lateral White Matter (of the spine): Lateral portion of the white matter, includes the descending corticospinal tract.

Lateral geniculate nucleus (LGN): A region of the thalamus which receives information from the retina and projects to primary visual cortex. Also called the LGN.

Lateral lemniscal nucleus: A cluster of cells responsive to sound. Found in the brainstem above the superior olivary nucleus and below the inferior colliculus.

Lateral superior olivary nucleus: A cluster of cells responsive to sounds. Localizes sound by comparing the amplitude of the sound at one ear with the amplitude of the sound at the other ear.

Lens: A part of the eye which adjusts the focus of an image to allow us to see near or far objects.

Lexical meaning: The meaning of a base word, independent of its use in another construction (for example, "play" is the lexical meaning of the words "plays," "played," and "playing").

Limbic System: A group of brain structures that work to regulate emotions, memory and certain aspects of movement. Includes the amygdala, hippocampus, cingulate gyrus, septum and basal ganglia.

Lobotomy: The surgical removal of a cortical lobe.

Long-term memory: A type of memory that lasts from a few hours to many years.

Long-term potentiation: A long-lasting increase in the efficacy of a synapse.

Longitudinal fissure: A deep sulcus (groove) that runs down the middle of the cortex and provides a prominent landmark for separating the brain into the left and right hemispheres.

Lou Gehrig's Disease: A common name for Amyotrophic Lateral Sclerosis (ALS), a disease that attacks the neurons of the brain and spinal cord. Typically, patients with ALS lose voluntary control over a period of years, and experience muscle atrophy.

Lower Brain: Term used to describe the evolutionarily older part of the brain.

Lumbar Level (of the spine): 3rd level of the spine following cervical and thoracic.

Luminal surface: The innermost layer of cortical cells, where mitosis takes place during cortical development.

Lymphocytes: A major class of white blood cells important in the immune response.

Macula: A photoreceptor-rich region in the center of the retina.

Macular degeneration: A retinal disease associated with old age, and characterized by a loss of cells from the macula.

Magnetic Resonance Imaging (MRI): A technique for imaging soft tissues, especially the brain, using magnets. While MRI provides a static image of the brain, a related technique called fMRI (functional magnetic resonance imaging) can image changing activity within the brain.

Magnocellular: The large cells in the thalamus that are involved in processing of rapidly changing information to the cerebral cortex.

Magnocellular layer: One of the two lower layers of the lateral geniculate nucleus, also called an M layer. M layer cells receive visual information that concerns motion.

Magnocellular pathway: A group of nerve fibers carrying high-contrast visual information, including information about motion in the visual field. The magnocellular pathway originates from M-type ganglion cells in the retina and terminates principally in the magnocellular layer of the lateral geniculate nucleus.

Malleus: one of the three middle ear bones -- the one closest to the eardrum.

Medial: Referring to a structure that is closer to the midline of another structure, as opposed to a lateral. For example, the medial part of an egg is the yolk, while the lateral part is the egg white.

Medial superior olivary nucleus: A cluster of cells responsive to sound. Localizes sound by comparing the time the sound arrives at one ear with the time it arrives at the other ear.

Medulla oblongata (myelencephalon): Located within the brainstem, or rhombencephalon (Hindbrain). Responsible for controlling respiration, circulation and other bodily functions.

Memory space theory: A theory of hippocampal function, suggesting that the hippocampus acts to encode environmental episodes rather than spaces in particular. As opposed to the cognitive map theory.

Meniere's Disease: Hearing and Balance problems resulting from a rupture of the basilar membrane.

Mesencephalon (Midbrain): Links forebrain and hindbrain; contains cerebral aqueduct.

Mesoderm: The middle layer of the three embryonic tissue layers first delineated during gastrulation; give rise to skeleton, circulatory system, muscles, and reproductive system.

Metalinguistic awareness: The abilities to think about language and comment on its characteristics and functions.

Metencephalon: Structure located in the rhombencephalon, or hindbrain. Origin of the pons and cerebellum.

Microgyria: One of several minor brain malformations that may be linked to reading disorders.

Midbrain: (See Mesencephalon)

Middle Ear: The part of the auditory system between the eardrum and the cochlea. This includes the ossicles.

Migration: The travelling of neural cells to an endpoint somewhere in the nervous system.

Mitosis: Nuclear division in eukaryotic cells leading to the formation of two daughter nuclei each with a chromosome complement identical to that of the original nucleus.

Mnemonic: A mental procedure used to assist recollection. For example, making up a rhyme to remember an address, or a bizarre image to remember a name.

Modality: A mode of sensation, for example, hearing, touch, smell, taste, or vision.

Modality-specific: A brain process specific to a type of sensory information, for example a process particular to hearing.

Monoamine oxidase inhibitors: Drugs that increase levels of neurotransmitters in the brain by preventing their decomposition.

Monaural: Relating to one ear.

Morphemes: The smallest unit in language that carries meaning. A morpheme can be a word or a word ending (like a grammatical ending, eg. past tense -ed.).

Morphine: an opioid drug that is used to attenuate pain.

Motor Cortex: A part of the brain that is responsible for executing movements of the body.

Motor Homunculus: A disproportionate map of the body representing the amount of motor cortex devoted to each body part.

Motor Program: A plan of action including the sequence of muscles needed and the level of contraction required for each muscle.

Mozart effect: An effect first described in 1993 by Drs. Gordon Shaw and Frances Rauscher, who showed that undergraduates who listened to 10 minutes of a Mozart sonata performed better on cognitive tests. The improvement lasted for around 10-15 minutes, and the implications of the finding are still debated.

Multiple Intelligences Theory: The view championed by Dr. Howard Gardner that intelligence is not a singular property, but "the potential to solve problems or to fashion products that are valued in at least one cultural context." (Gardner, 1983).

Muscle Fiber: Single, elongated cell in skeletal muscle.

Muscle Spindle: Stretch receptor within skeletal muscles which provides information about the length of the muscle.

Myelencephalon: Located in the hindbrain and origin of the medulla oblongata.

Myelin: A glassy, white sheath surrounding the axons of some neurons. Myelin acts as an insulator, and helps neural signals travel more quickly and over greater distances than they could in an uninsulated axon. Myelin is composed of Schwann cells that wrap themselves concentrically around the neural axon.

Myelination: The process of insulating axons in the nervous system.

Myopia: Also known as nearsightedness because near objects appear in focus while far objects are blurry. Myopia is the result of an overly long eyeball. The majority is functional or often called school Myopia felt to have been complicated by close demanding work.

Natural Selection: A theory stating that individual organisms that survive to produce viable offspring pass on the genes that made the survival possible. On average, the fittest traits in a population are thereby transmitted to descending generations causing the selection for fitness to drive the evolution of the species.

Neocortex: Literally meaning "new cortex," because it evolved later than other brain areas. Also known as isocortex. Located in the dorsal, or front part of the brain, the neocortex is especially large in higher primates and is responsible for sensory and motor processing as well as abstract reasoning and association.

Neospinothalmic Tract: a bundle of nerve fibers in the spinal cord that carries mixed sensory and motor information. Neural crest cells: Cells that mirgrate away from the neural tube to form a variety of peripheral tissues.

Neural groove: In development, the stage just before the neural plate closes to form the neural tube.

Nerve Growth Factor: A neurotrophin that is typically found in the peripheral nervous system, and the first neurotrophin discovered.

Neural plate: A thickened strip of ectoderm along the dorsal side of the early vertebrate embryo; gives rise to the central nervous system.

Neural tube: Formed during development when the neural plate folds in on itself.

Neurodegenerative Diseases: Any disease which causes a slow decay of the nervous system and its activity, for example, Alzheimer's disease.

Neuroepithelium: The cells inside the nerual tube that go on to form the brain and spinal cord.

Neuron: The cellular unit of the central and peripheral nervous systems. Neurotransmitter: A chemical released by neurons to relay information to other cells.

Neurotrophins: Powerful molecules that affect the survival, growth, and differentiation of neurons, for example, Nerve Growth Factor (NGF) and Brain-Derived Neurotrophic Factor (BDNF).

Newton, Sir Isaac: (1642-1727) English physicist and mathematician most often remembered for his Law of Gravity, which is said to have been brought about by his witnessing a falling apple. Among his many other accomplishments, he deduced that white light is a mixture of colors, and he devised the first reflecting telescope.

Nondeclarative memory: A type of memory that cannot be verbally recalled, also called procedural memory. For example, catching a baseball or riding a bicycle.

Norepinephrine: a neurotransmitter arising principally from neurons located in the locus ceruleus and projecting to many areas of the brain, including the limbic system. Deficient amounts of norepinephrine are associated with depression, and overabundant amounts with mania.

Nucleus: 1. An intracellular organelle that houses the cell’s DNA; 2. In neuroanatomy, a group of neurons that acts together to perform a specific function, most often referring to neurons in the brainstem.

Nursery Rhyme Effect: the effect achieved by introducing children to patterns of sounds, through nursery rhymes and early stories, so the child's brain receives the input it will need to categorize words by their internal structure.

Nystagmus: Rhythmic oscillation of the eyeballs, usually horizontally. Caloric nystagmus is a normal reaction to cold or warm water squirted into the ear; nystagmus can also be induced by rapidly turning the head to one side.

Occipital Lobe: Mostly devoted to vision. Contains the primary visual cortex . Delineated by the preoccipital notch and the parieto-occipital sulcus.

Occipital Notch: A sulcus, or groove, within the cerebral cortex that marks the ventral boundary of the occipital lobe.

Ocular dominance column: A stack of cells in primary visual cortex that receives input from only one of the two eyes.

Oculomotor nerve (CN III): The third cranial nerve, responsible for movement of the eye in its orbit. See the Cranial Nerve Table.

Off-Center: A receptive field shaped like two concentric discs, in which stimuli in the center disc are inhibitory and stimuli in the outer disc are excitatory. Off-center fields occur in bipolar and ganglion cells in the retina, as well as in M and P layer cells of the lateral geniculate nucleus.

Olfactory: Of or relating to the sense of smell.

Olfactory nerve (CN I): The first cranial nerve, responsible for the sense of smell. See the Cranial Nerve Table.

Olfactory Tract: Nerve route that carries the sense of smell from the olfactory bulb to the cerebral cortex.

Oligodendrocytes: Glial cells that myelinate the central nervous system axons.

On-Center: A receptive field shaped like two concentric discs, in which stimuli in the center disc are excitatory and stimuli in the outer disc are inhibitory. On-center fields occur in bipolar and ganglion cells in the retina, as well as in M and P layer cells of the lateral geniculate nucleus.

Onset: an optional part of a syllable that contains any consonant sounds which precede the vowel. For example, in "bet" the onset is b-, while in "spoke" the onset is sp-. Some syllables, such as "it", do not contain onsets.

Optic chiasm: The point at which the optic nerves from each eye meet and partially cross hemispheres.

Optic nerve: The second cranial nerve. A thick bundle of nerve fibers (axons from ganglion cells) extending from the retina to the thalamus. See the Cranial Nerve Table.

Orbitofrontal Cortex (aka Brodmann's Area 47): A region of the frontal cortex which is involved in motor function and communicates with the basal ganglia as well as other limbic structures. This structure may be involved in mood-related disorders as well as motor dysfunction.

Orientation column: A stack of cells in primary visual cortex that all respond best to lines of the same orientation.

Ossicles: The three bones in the middle ear.

Otitis Externa: Inflammation of the outer ear resulting from infection or physical injury.

Otitis Media: Infection of the inner ear which blocks the eustachian tube and puts pressure on the ear drum.

Otosclerosis: The overgrowth of bones in the middle ear, most commonly, the stapes.

Outer ear: The cartilage that guides sound into the ear canal and the ear canal. The pinna.

Oval Window: An opening into the scala vestibuli of the cochlea, the oval window is covered by a membrane. The stapes fits into the oval window.

Paleospinothalamic Tract: a bundle of nerve fibers in the spinal cord that carries mixed sensory and motor information.

Panic Disorder: An anxiety disorder characterized by strong somatic symptoms of fear (increased heart rate, sweating, etc.) that come on with no apparent trigger.

Papillae: Small protuberances that cover the top and side surfaces of the tongues. The papillae contain the taste buds.

Parasympathetic ganglia: A collection of neurons in the parasympathetic nervous systems.

Paraventricular Nucleus: A nucleus within the hypothalamus that regulates the release of hormones from the pituitary gland.

Parietal Lobe: Contains somatosensory areas and sensory integration areas. Separated from the frontal lobe by the central sulcus, separated from occipital lobe by the parieto-occipital sulcus.

Parieto-occipital sulcus: A groove within the cerebral cortex that marks the dorsal boundary between the occipital and parietal lobes.

Parkinson's disease: A degenerative disease of the nervous system characterized by muscle tremors, altered gait, and partial paralysis.

Parvocellular Layer: One of the four upper layers of the lateral geniculate nucleus, also called a P layer. P layer cells receive visual information about color and fine structure.

Pathway: A route of information flow in the nervous system.

PDD-NOS (Pervasive Developmental Disorder, Not Otherwise Specified): A diagnosis given to individuals who do not meet the criteria for autism in one of its three categories.

Perfect pitch: The capacity to recognize and name any note on the musical scale (i.e., middle C, E flat, A sharp) without hearing it in relation to other notes.

Perilymph: Fluid in the scala vestibuli and scala media.

Perinatal: Relating to the time just before, during, and just after birth.

Peripheral Nervous System: Located outside the brain and spinal cord. Obtains sensory information from the external world and provides motor output to the voluntary muscles that allow us to move.

Perirhinal cortex: evolutionary older cortex in the temporal lobes, located near the hippocampus; may be involved in learning and memory.

Pervasive Developmental Disorder: A severe disruption in a child's cognitive, behavioral, social and emotional growth that results in widespread distortion of the processes of development; example: childhood autism.

Phase-lock: A correspondence between the activities of two oscillating events. If these activities are represented as waves, then the peaks of the waves will be correlated at regular intervals. In the auditory system, the response of hair cells in the basilar membrane is phase-locked to low frequency sound waves.

Phase-shift: When the activity of one cycling event is displaced in time, or shifted, from the activity of another cycling event. If these activities are represented as waves, then one wave will lead the other.

Phonemic awareness: The ability to distinguish amongst the smallest sounds in language that can change meaning.

Phonemes: The smallest recognizable speech sounds and root of all spoken language. When added together, phonemes create syllables, which allows the creation of words.

Phonological skills: The ability to recognize and use all sizes of sound units, such as words, syllables and phonemes. Phonological processing, and particularly phonemic awareness, is a critical skill for learning to read or becoming a better reader.

Phonology: A language's sound system, including the rules for combining sounds to produce meaningful utterances.

Phosphenes: Spots of light that are produced when pressure is placed on the eyeball.

Photoreceptor: A cell in the retina which can convert light into electrochemical signals.

Photosynthesis: The process by which green plants and certain other organisms transform light energy into chemical energy.

Phrenology: The study of using bumps on the skull to determine human behavior and characteristics.

Phylogenetic: Measured across species, a way of determining the chronological appearance of biological features (i.e., the older the species in terms of evolution, the longer the feature has been around).

Pial surface: The outermost layer of cortical cells.

Pineal gland: An endocrine gland located in the cerebrum, which regulates the production of the hormone melatonin.

Pinna: The cartilage that guides sound into the ear canal.

Pituitary Gland: A small gland at the base of the brain which secretes hormones that regulate most of the other glands in the body. Often referred to as the "master gland."

Place cell: A term used to describe neurons in the rat hippocampus that appear to respond preferentially to discrete places in an environment.

Place field: The receptive field of a place cell. The place field of a place cell is a spot in the environment that the place cell responds to most strongly.

Placenta: A fetal organ, approximately 9 inches in diameter, that is tightly attached to the inner lining of the uterus. The placenta consists of a root-like complex of fetal vessels coming from the uterine wall, bathed in maternal blood and supplied with fetal blood through the umbilical cord. The placenta is responsible for delivering nutrients from the mother to the fetus.

Planum Temporale: A cluster of neurons believed to be important for language processing; in most people, it is larger in the left hemisphere than in the right.

Plasticity: The ability of a neural network to be reconfigured or rewired; changing connections within a neural network.

Polysomnography: The study of sleep using measures of electrical brain activity, eye movements, and muscle activity.

Pons: A structure at the top of the brain stem containing a number of nuclei and many fiber tracts connecting the cerebellum and medulla to the higher brain areas.

Posterior Parietal Cortex: Posterior portion of the parietal cortex involved in transforming visual information to motor commands.

Positron Emmision Tomography (PET): A technique for imaging brain activity using radioactive dyes injected into the bloodstream.

Post-Encephalitic Parkinson's Disease: Name used to describe the mysterious "sleeping sickness" that evolved out of the encephalitis epidemic of the 1920s.

Postsynaptic: On the receiving side of the synapse. A postsynaptic cell receives neurotransmitter from a presynaptic neuron.

Post-traumatic Stress Disorder (PTSD): A disorder that causes people to relive emotionally stressful events as though they were actually occurring; most common in rape victims, disaster survivors and war veterans.

Precentral Gyrus: Bump of cortex in the frontal lobe located anterior to the central sulcus, site of the primary motor cortex.

Prefrontal Cortex: An area of the brain associated with higher cognitive functions including planning and working memory.

Prefrontal Lobes: The front part of the brain, associated with complex decision-making, behavioral inhibition, and judgement.

Premotor Cortex: Region of cortex in the frontal lobe involved in the sensory guidance of movement and activating proximal and trunk muscles. Prenatal: Relating to the time before birth.

Presbyopia: A condition in which the eye’s lens thickens and loses its ability to contract as a result of aging. Presbyopia is optically similar to hyperopia because it causes difficulty in focusing on near objects.

Presynaptic: On the sending side of the synapse. A presynaptic neuron secretes neurotransmitter onto a postsynaptic target cell.

Pretectum: A nucleus in the midbrain that controls the pupillary light reflex. Primary-like response pattern: An activity pattern exhibited by some neurons in the cochlear nucleus. The primary-like response pattern is characterized by a large burst of action potentials at the stimulus onset, followed by little activity for the stimulus duration.

Primary Motor Cortex: Cortical area in the frontal lobe which is directly involved in producing muscle contraction.

Primary Visual Cortex: Located in the occipital lobe. Receives the earliest information from the eyes by way of the thalamus. Also called Brodmann Area 17, after the anatomist who identified the region, or Striate Cortex, because in cross section the primary visual cortex has a distinct band of white myelin within the cell layer.

Procedural memory: a type of unconscious memory for motor skills that does not require the hippocampus for formation.

Progenitor cells: Cells of a specific type that give rise to many other cells of the same kind.

Proprioception: Sensation of movement in joints and muscles.

Prosencephalon (Forebrain): Believed to be the site of the highest intellectual functions. Includes structures such as the thalamus, hypothalamus, and the cerebral cortex.

Prosopagnosia: An inability to recognize faces following brain injury.

Prozac: A trademark for an antidepressant drug that inhibits the uptake of serotonin by the central nervous system.

Psychometric: measurement of mental processes.

Psychophysical study: Psychological tests which determine behavioral responses to certain physical stimuli–such as behavioral responses to tastes or to sounds.

Pupil: A hole in the middle of the iris which can be dilated or constricted to adjust the amount of light that shines on the retina.

Pupillary light reflex: The response of the pupil to changing lighting conditions. The pupil constricts in response to bright light, and dilates in response to dim light. In the direct pupillary light reflex, light shining into one eye causes the ipsilateral pupil to constrict. In the consensual pupillary light reflex, light shining into one eye causes the contralateral pupil to constrict.

Putamen: a nucleus of the basal ganglia located deep within the brain. The putamen is involved in sensorimotor integration and motor control.

Radial glial cells: Connective tissue cells that guide the migration of neurons during development.

Raphé nuclei: Groups of cells located in the brain stem that have been implicated in sleep behavior.

Rapid eye movement (REM) sleep: A sleep state that occurs about every 90 minutes through the night; characterized by frequent eye movements and often associated with dreaming.

Receptive field: The set of stimulus characteristics that a neuron responds to optimally. For visual neurons, this might be a particular shape or a particular region of space. For auditory neurons, it might be a particular range of sound frequencies.

Reinforcement: The use of reward, encouragement, and repetition to promote learning and memory.

Reissner's membrane: Membrane separating the scala vestibuli from the scala media.

Relativism: The theory that morals and truth are not universal, but are relative to the groups holding them.

Resonant frequency: Energy delivered to an oscillating system at the resonant frequency will increase the amplitude of the oscillations. For example, when a child is on a swing, she tends to time her kicks to the resonant frequency of the swing so that she can go higher.

Reticular formation: A network of neurons that are part of the brainstem; mediates aspects of arousal.

Retina: A sheet of tissue at the back of the eye which converts light into electrochemical signals, pre-processes those signals to detect contrast changes, edges, and color, and then sends the pre-processed information on to the brain.

Retinitis pigmentosa: An inherited condition in which the retina's rod cells degenerate, resulting in the loss of peripheral and night vision.

Retinotopic: Organized in a point-to-point representation of the retina.

Retrograde amnesia: A condition resulting from injury or disease in which the patient forgets events ocurring prior to the injury, but can remember events that occur after the injury.

Retrograde Signal: A neural signal that is transported in the opposite direction of normal electrochemical impulses, e.g. from a postsynaptic neuron to a presynaptic neuron.

Rett's Disorder: A pervasive developmental disorder related to autism; a progressive neurological disorder occurring in females only.

Reuptake: the process by which a neuron returns certain amounts of a neurotransmitter back to the neuron that released it.

Rhombencephalon (Hindbrain): Often referred to as the brainstem. Includes the pons, cerebellum and medulla oblongata.

Rime: An obligatory part of a syllable that contains the vowel and any consonant sounds that follow it. For example, in "bet" the rime is -et. Single-syllable words with the same rime typically rhyme with one another: bat, sat, flat, and splat all contain the rime -at.

Ritalin: A brand name form of the drug methylphenidate, a mild central nervous stimulant used in the treatment of narcolepsy in adults and attention deficit disorder in children.

Rod cell: A type of photoreceptor in the retina which is insensitive to color. Rod cells are very sensitive to dim light, and are responsible for our night vision.

Round window: A membrane covered opening at the base of the cochlea opening into the scala tympani.

Saccade: A high velocity eye movement from one point to another point. When primates pan their gaze over a scene, their eyes move in saccades rather than in a continuous, smooth motion.

Saccule: Along with the utricle, a vestibular organ in the inner ear. Specifically, the saccule responds to vertically directed movement.

Scala media: The middle compartment of the cochlea. Contains the endolymph which surrounds the cilia of the hair cells.

Scala tympani: One of the compartments of the cochlea. Contains endolymph. One end is the round window, the other end is continuous with the scala vestibuli through the helicotrema.

Scala vestibuli: One of the compartments of the cochlea. Contains perilymph. One end is the oval window, the other end is continuous with the scala tympani through the helicotrema.

Schema: A term introduced by Jean Piaget that refers to an internal representation of external experience in terms of a symbol, a representational outline, a percept or a concept.

Schizophrenia: A neuropsychological disorder characterized by any combination of inappropriate affect, hallucinations, delusions, and psychotic episodes. Development of schizophrenia has a genetic component, and is associated with excess dopaminergic transmission.

Schwann cells: Cells which wrap around nerve fibers to form myelin, an electrical insulator.

Scoville units: A system of units used to rate the "hotness" of chili peppers.

Secondary Motor Cortices: Regions of cortical motor function besides the primary motor cortex; posterior parietal cortex, premotor cortex, supplementary motor area.

Secondary Visual cortex: Also called V2, responsible for perceiving color and form.

Selective Serotonin Reuptake Inhibitor (SSRI): a class of drugs, used to treat depression, that regulate the movement of serotonin in the nervous system. Examples include Luvox, Paxil, Prozac, and Zoloft.

Semantics: The expressed meaning of sentences, and words.

Semicircular canals: A fluid-filled part of the cochlea. Tiny hair cells in these canals detect the motion of the fluid, providing information that gives our brain a sense of balance and head position.

Sensorineural hearing loss: Hearing loss due to problems in the cochlea where the mechanical signal is changed to an electrical signal.

Separation Anxiety: A universal fearful response to separation often from a parent. Septum: part of the limbic system; located on the midline just in front of the hypothalamus.

Serotonin: The oldest neurotransmitter in the brain; important for emotional processing and sleep

Soma: The main part of a neuron cell; term comes from the Greek word for "body."

Somatic Nervous System: Also called the voluntary nervous system, the somatic nervous system is a component of the peripheral nervous system that controls voluntary actions by carrying signals to skeletal muscles to make them contract.

Somatic marker: An association between a type of event and an emotional response, which is stored in memory.

Somatosensory: Relating to information perceived through sensory organs in the skin and muscles including tactile, temperature, pressure, and position information.

Somatotopic: Organized in a point-to-point representation of the surface of the body.

Spastic palsy: A type of motor control disorder characterized by stiff, awkward movement.

Spatial memory: A type of memory concerned with representing physical places.

Spatial-temporal intelligence: The ability to see patterns in space and time, or to form mental images from physical objects and to manipulate (i.e., rotate, or turn) such images in one's mind.

Sperry, Roger (1913 — 1994): Neurophysiologist who conducted Nobel-prize-winning research into brain hemisphere laterality.

Spina bifida: A developmental disorder that results when the neural tube fails to close at the back end; outcomes vary depending on how much of the spinal cord is disrupted.

Spinal accessory nerve (CN XI): The eleventh cranial nerve, innervating the larynx and the muscles of the neck. See the Cranial Nerve Table.

Spinal cord: A large bundle of nerve fibers beginning at the base of the brainstem and continuing down to the tail bone. The spinal cord is a part of the central nervous system, and most of the fibers within it serve motor and sensory functions.

Split-Brain: The surgery in which the corpus callosum is completely severed to prevent the spread of intractable epilepsy across the brain. A split-brain patient is one who has undergone the surgery.

Stapes: One of the three middle ear bones -- the one farthest from the eardrum and closest to the oval window.

Stereognosis: The ability to recognize objects by sense of touch. Robert Sternberg: Yale psychologist responsible for the Triarchic Theory of Intelligence, which poses that three facets make up what we call intelligence, including analytical, creative and practical intelligences.

Strabismus: Also called "lazy eye", strabismus is a failure of both eyes to maintain the same direction of gaze. The disparity of the images entering the eyes causes one eye to be favored; the result of prolonged strabismus is amblyopia.

Stretch Receptor: Structure reporting the degree of stretch.

Striate cortex: Structure located in the occipital lobe that, in cross section, has a distinct band of white myelin within the cell layer. Also called Brodmann Area 17, after the anatomist who identified the region, : or : V1, primary visual cortex, because it receives the earliest information from the eyes by way of the thalamus.

Stroke: A sudden, acute attack or injury.

Stroop Effect: A type of cognitive interference first described by Dr. J.R. Stroop in 1935. The Stroop Effect is an increase in reaction time evident when a subject has to identify one stimulus property that conflicts with a more salient stimulus property. For example, if the word "blue" is written in red ink, a subject will have a hard time identifying the ink color.

Stroop task: A test that measures cognitive interference, the role that one stimulus characteristic plays in the perception of another characteristic.

Subcortical: Literally located beneath the cortex, referring to brain structures that are not a part of the cerebral cortex.

Subitization: The process of directly perceiving the number of a collection of items, as distinct from counting.

Substantia nigra: A nucleus of the basal ganglia named for its dark pigmentation in cross sections. Parkinson's disease is characterized by a loss of cells in this nucleus.

Subthalamic nucleus: A group of neurons that resides just below the thalamus and comprises part of the basal ganglia. These neurons are in communication with neurons in the globus pallidus, and are a target for electrical stimulation in the treatment of Parkinson's disease.

Sulci (singular, Sulcus): Grooves within the convolutions of cerebral cortex, the deepest of which are sometimes called fissures.

Superior colliculus: A nucleus in the midbrain which controls saccadic eye movements. The superior colliculus is also responsible for turning the head and eyes to see a stimulus that is heard or felt.

Superior olivary nuclei: A group of nuclei including the lateral superior olivary nucleus and the medial superior olivary nucleus, two auditory nuclei that are involved in sound localization.

Supplementary Motor Area (SMA): Region of cortex in the frontal lobe involved in the planning of complex movements and in two-handed movements.

Suprachiasmatic nucleus (SCN): A group of cells in the hypothalamus that are important for the maintenance of biological rhythms.

Sympathetic ganglia: Collections of neurons in the symapathetic nervous system.

Synapse: The physical structure that makes an electrochemical connection between two neurons.

Synaptic proliferation: a process in which the developing brain creates numerous connections between neurons (synapses) to prepare the brain for new experiences.

Synaptic pruning: A process in which the brain removes ineffective connections between neurons to make the remaining connections more efficient.

Syntax: The structure of a language, or the rules which specify how grammatical markers and words are combined to make meaningful sentences.

Telencephalon: Located in the forebrain and associated with perception and initiation of action. Believed to be the site of the highest intellectual functions and the origin of the entire cerebral cortex.

Temporal lobe: Primarily responsible for hearing and memory/learning. Separated from the frontal lobe by the lateral sulcus.

Tastant molecule: A molecule that can be sensed by cells in the taste buds.

Taste Receptor Cells: Cells in the tongue which can sense molecules that carry taste information. These cells respond to these tastant molecules by changing their internal calcium concentration. This response is then communicated to nearby nerves, which communicate the signal to the brain.

Taste modality: One of the five tastes that humans are known to perceive. These five tastes are: salt, sour, sweet, bitter, and the taste named umami, which is the taste of monosodium glutamate–MSG.

Thalamocortical pathway: A fiber tract leading from the thalamus to the cerebral cortex.

Thalamus: A structure in the brain that traffics sensory information such as vision, hearing and touch coming into the brain and distributes that information to appropriate areas of the cerebral cortex.

Tinnitus: A ringing in the ear.

Tissue: A sheet of morphologically similar cells which acts together to perform a function. Tissue is categorized into the four basic types of muscle, nerve, epidermal, and connective.

E.L. Thorndike (1874-1949): American psychologist who pioneered the study of animal intelligence. The author of some 450 books and articles, Thorndike was an influential force in twentieth century educational psychology.

Thrombus: A blood clot composed of platelets, fibrin, and red and white blood cells.

Tinnitus: Ringing of the ears.

Tonotopic: Organized in a progression of increasing sound frequencies.

Transcranial magnetic stimulation (TMS) : A cortical stimulation technique. Electromagnets outside the head create fluctuating magnetic fields that induce electric currents in specific areas of the brain.

Transcutaneous Electrical Nerve Stimulation (TENS): a technique that uses a low powered electrical device to stimulate nerve fibers without penetrating the skin. TENS is typically used for pain management.

Transfer: The application of past learning to new learning, and the extent to which new learning will be useful, or generalized, to future learning.

Transmutation: Jean-Baptiste Lamarck's 19th Century theory that the billions of species on earth evolved by separating from each other from some central point of origin.

Transporter: a molecule on the surface of a neuron that returns certain amounts of a neurotransmitter back to the neuron that released it.

Trapezoidal body: One of the auditory nuclei in the brainstem.

Triarchic Theory of Intelligence: Theory of intelligence which posits that there are three main kinds of intelligence: analytical, creative and practical.

Tricyclic antidepressants: Drugs that increase the levels of neurotransmitter in the brain, especially serotonin; often used to treat depression.

Trigeminal nerve (CN V): The fifth cranial nerve, responsible for general sensation of the face, and for chewing. See the Cranial Nerve Table.

Trochlear nerve (CN IV): The fourth cranial nerve, innervating the superior oblique muscle, which rotates the eye downward and outward. See the Cranial Nerve Table.

Trophic Factors: An important class of molecules that causes cells to grow or survive. Examples include molecules such as Fibroblast Growth Factor (FGF) and Platelet-Derived Growth Factor (PDGF). Tumor: An abnormal growth of cells.

Tympanogram: Record of ear drum movement.

Unconditioned Stimulus (US): In classical conditioning, a stimulus that naturally and automatically triggers a response--no learning required.

Unipolar disorder: major depressive illness, symptoms of which include sad mood, insomnia, feelings of guilt, and thoughts of suicide.

Utricle: Along with the saccule, a vestibular organ in the inner ear. Specifically, the utricle responds to linear acceleration in the horizontal direction or tilting of the head.

Vagus nerve (CN X): The tenth cranial nerve, responsible for swallowing and control of the larynx. See the Cranial Nerve Table.

Ventral: In humans, closer to the front of the body, the belly side.

Ventral Horn (of the spine): Location in the spine where corticospinal fibers synapse, neurons are involve in motor function.

Ventromedial nucleus: a nucleus in the hypothalamus responsible for metabolic regulation.

Vertigo: Dizziness.

Vestibular: Referring to balance.

Vestibular nerve: A division of the vestibulocochlear nerve that conveys information about the sense of balance from the ear to the brainstem.

Vestibulocochlear nerve (CN VIII): See auditory nerve. Visceral nervous system: Also known as the autonomic nervous system. Receives input from, and sends output to, our internal organs. Responsible for controlling involuntary functions such as blood flow, breathing and digestion.

Visual cortex: Any area of the cerebral cortex principally associated with vision.

Visual Field: The visible area, typically measured in degrees from a line through the center of the head.

Visuospatial Perception: The perception of an object and its movement through space.

Vitreous humor: Literally "glass-like fluid," vitreous humor is a thick liquid which fills up most of the eyeball. It is contained between the lens and the retina.

Phillip Vogel: U.S. surgeon involved in the development of successful commissurotomy for the treatment of epilepsy in the early 1960s. Voluntary nervous system: Also called the somatic nervous system, the voluntary nervous system is a component of the peripheral nervous system that controls voluntary actions by carrying signals to skeletal muscles to make them contract.

Carl Wernicke (1848-1905): German neurobiologist who studied brain damage, particularly the form of aphasia in which language comprehension is impaired. Discovered the region of the brain involved in this illness, now known as Wernicke's Area.

Wernicke's area: An area of the left temporal lobe that is crucial for language comprehension.

Working memory: A type of memory where information is readily available for a very short period of time; also called "scratch-pad" memory.

Zeitgebers: German term for "time givers," meant to describe exogenous cues that allign our internal clocks.

Zygote: The cell created by the union of two gametes, in which the gamete nuclei are also fused; the earliest stage of the diploid generation.