G-1

A

absolutely refractory The state of an axon in the repolarizing period, during which a new action potential cannot be elicited (with some exceptions), because gate 2 of sodium channels, which are not voltage sensitive, are closed.

acetylcholine (ACh) First neurotransmitter discovered in the PNS and CNS; activates skeletal muscles in the SNS; may either excite or inhibit internal organs in the ANS.

action potential Large, brief reversal in the polarity of an axon membrane.

activating system Neural pathways that coordinate brain activity through a single neurotransmitter; its cell bodies lie in a brainstem nucleus; axons are distributed through a wide CNS region.

addiction Desire for a drug; manifested by frequent use, leading to physical dependence in addition to abuse; often associated with tolerance and unpleasant, sometimes dangerous, withdrawal symptoms on cessation. Per the DSM-5, called substance use disorder.

afferent Conducting toward a CNS structure.

agonist Substance that enhances synapse function.

akathesia Small, involuntary movements or changes in posture; motor restlessness.

allele Alternative form of a gene; a gene pair contains two alleles.

alpha rhythm Regular wave pattern in an electroencephalogram; found in most people when they are relaxed with eyes closed.

Alzheimer disease Degenerative brain disorder related to aging that first appears as progressive memory loss and later develops into generalized dementia.

amblyopia Condition in which vision in one eye is reduced as a result of disuse; usually caused by a failure of the two eyes to look in the same direction.

amnesia Partial or total loss of memory.

amphetamine Drug that releases the neurotransmitter dopamine into its synapse and like cocaine, blocks dopamine reuptake.

amplitude Stimulus intensity; in audition, roughly equivalent to loudness, graphed by the increasing height of a sound wave.

amusia Tone deafness—inability to distinguish between musical notes.

amygdala Almond-shaped collection of nuclei in the limbic system; plays a role in emotional and species-typical behaviors.

anabolic steroid Class of synthetic hormones related to testosterone that have both muscle-building (anabolic) and masculinizing (androgenic) effects; also called anabolic–androgenic steroid.

androgen Class of hormones that stimulates or controls masculine characteristics and level of sexual interest.

anencephaly Failure of the forebrain to develop.

anomalous speech representation Condition in which a person’s speech zones are located in the right hemisphere or in both hemispheres.

anorexia nervosa Exaggerated concern with being overweight that leads to inadequate food intake and often excessive exercising; can lead to severe weight loss and even starvation.

antagonist Substance that blocks synapse function.

anterior spinothalamic tract Pathway from the spinal cord to the thalamus that carries information about pain and temperature.

anterograde amnesia Inability to remember events subsequent to a disturbance of the brain such as head trauma, electroconvulsive shock, or neurodegenerative disease.

antianxiety agent Drug that reduces anxiety, including minor tranquilizers such as benzodiazepines and sedative-hypnotic agents.

aphagia Failure to eat; may be due to an unwillingness to eat or to motor difficulties, especially with swallowing.

aphasia Inability to speak or comprehend language despite the presence of normal comprehension and intact vocal mechanisms. Broca’s aphasia is the inability to speak fluently despite the presence of normal comprehension and intact vocal mechanisms. Wernicke’s aphasia is the inability to understand or to produce meaningful language even though word production remains intact.

apoptosis Genetically programmed cell death.

apraxia Inability to make voluntary movements in the absence of paralysis or other motor or sensory impairment, especially an inability to make proper use of an object.

association cortex Neocortex outside primary sensory and motor cortices; functions to produce cognition.

associative learning Linkage of two or more unrelated stimuli to elicit a behavioral response.

astrocyte Star-shaped glial cell that provides structural support to CNS neurons and transports substances between neurons and blood vessels.

atonia Lacking tone; condition of complete muscle inactivity produced by motor neuron inhibition.

attention Narrowing or focusing awareness to a part of the sensory environment or to a class of stimuli.

attention-deficit/hyperactivity disorder (ADHD) Developmental disorder characterized by core behavioral symptoms, including impulsivity, hyperactivity, and/or inattention.

auditory flow Change heard as a person and a source of sound move relative to one another.

autism spectrum disorder (ASD) Range of cognitive symptoms from mild to severe that characterize autism; severe symptoms include greatly impaired social interaction, a bizarre and narrow range of interests, marked abnormalities in language and communication, and fixed, repetitive movements.

autoimmune disease Illness resulting from an abnormal immune response by the body against substances and tissues normally present in the body.

autonomic nervous system (ANS) Part of the PNS that regulates the functioning of internal organs and glands.

autoreceptor Self-receptor in a neuronal membrane; that is, it responds to the same transmitter released by the neuron.

axon Root, or single fiber, of a neuron that carries messages to other neurons.

axon collateral Branch of an axon.

axon hillock Juncture of soma and axon.

B

back propagation Reverse movement of an action potential into the soma and dendritic field of a neuron; postulated to play a role in plastic changes that underlie learning.

barbiturate Drug that produces sedation and sleep.

basal ganglia Subcortical forebrain nuclei that coordinate voluntary movements of the limbs and body; connected to the thalamus and to the midbrain.

basic rest–activity cycle (BRAC) Recurring cycle of temporal packets, about 90-minute periods in humans, during which an animal’s level of arousal waxes and wanes.

basilar membrane Receptor surface in the cochlea that transduces sound waves into neural activity.

behavioral myopia “Nearsighted” behavior displayed under the influence of alcohol: local and immediate cues become prominent; remote cues and consequences are ignored.

behavioral neuroscience Study of the biological bases of behavior in humans and other animals.

behavioral sensitization Escalating behavioral response to the repeated administration of a psychomotor stimulant such as amphetamine, cocaine, or nicotine; also called drug-induced behavioral sensitization.

behavioral therapy Treatment that applies learning principles, such as conditioning, to eliminate unwanted behaviors.

beta (β) rhythm Fast brain wave activity pattern associated with a waking EEG.

bilateral symmetry Body plan in which organs or parts present on both sides of the body are mirror images in appearance. For example, the hands are bilaterally symmetrical, whereas the heart is not.

binding problem Philosophical question focused on how the brain ties single and varied sensory and motor events together into a unified perception or behavior.

biological clock Neural system that times behavior.

biorhythm Inherent timing mechanism that controls or initiates biological processes.

bipolar disorder Mood disorder characterized by periods of depression alternating with normal periods and periods of intense excitation, or mania.

bipolar neuron Sensory neuron with one axon and one dendrite.

blind spot Retinal region where axons forming the optic nerve leave the eye and blood vessels enter and leave; has no photoreceptors and is thus said to be blind.

blob Region in V1 that contains color-sensitive neurons, as revealed by staining for cytochrome oxidase.

blood–brain barrier Tight junctions between the cells that compose blood vessels in the brain, providing a barrier to the entry of an array of substances, including toxins, into the brain.

brain connectome Map of the complete structural and functional fiber pathways of the human brain in vivo.

brainstem Central structure of the brain; responsible for most unconscious behavior.

Broca’s area Anterior left hemisphere speech area that functions with the motor cortex to produce movements needed for speaking.

C

carbon monoxide (CO) Gaseous neurotransmitter; activates cellular metabolism.

cataplexy State of atonia, as in REM sleep, occurring while a person is awake and active; linked to strong emotional stimulation.

cell adhesion molecule (CAM) A chemical molecule to which specific cells can adhere, thus aiding in migration.

cell assembly Hypothetical group of neurons that become functionally connected via common sensory inputs; proposed by Hebb as the basis of perception, memory, and thought.

cell body (soma) Core region of the cell containing the nucleus and other organelles for making proteins.

central nervous system (CNS) The brain and spinal cord, which together mediate behavior.

cerebellum Major brainstem structure specialized for learning and coordinating movements; assists the cerebrum in generating many behaviors.

cerebral cortex Thin, heavily folded film of nerve tissue composed of neurons that is the outer layer of the forebrain. Also called neocortex.

cerebral palsy Group of disorders that result from brain damage acquired perinatally (at or near birth).

cerebral voltammetry Technique used to identify the concentration of specific chemicals in the brain as animals behave freely.

G-2

cerebrospinal fluid (CSF) Clear solution of sodium chloride and other salts that fills the ventricles inside the brain and circulates around the brain and spinal cord beneath the arachnoid layer in the subarachnoid space.

cerebrum (forebrain) Major structure of the forebrain that consists of two mirror image hemispheres (left and right) and is responsible for most conscious behavior.

channel Opening in a protein embedded in the cell membrane that allows the passage of ions.

chemical synapse Junction at which messenger molecules are released when stimulated by an action potential.

chemoaffinity hypothesis Proposal that neurons or their axons and dendrites are drawn toward a signaling chemical that indicates the correct pathway.

chemogenetics Transgenic technique that combines genetics and synthetic drugs to activate targeted cells in living tissue.

cholinergic neuron Neuron that uses acetylcholine as its main neurotransmitter; cholinergic applies to any neuron that uses ACh as its main transmitter.

chordate Animal that has both a brain and a spinal cord.

chronic traumatic encephalopathy (CTE) Progressive degenerative disease caused by multiple concussions and other closed-head injuries, characterized by neurofibrillary tangles, plaques, cerebral atrophy, and expanded ventricles due to cell loss.

chronotype Individual differences in circadian activity.

circadian rhythm Day–night rhythm.

cladogram Phylogenetic tree that branches repeatedly, suggesting a taxonomy of organisms based on the time sequence in which evolutionary branches arise.

clinical trial Consensual experiment directed toward developing a treatment.

cochlea Inner ear structure containing the auditory receptor cells.

cochlear implant Electronic device implanted surgically into the inner ear to transduce sound waves to neural activity and allow a deaf person to hear.

cognition Act or process of knowing or coming to know; in psychology, refers to thought processes.

cognitive-behavioral therapy (CBT) Problem-focused, action-oriented, structured treatment for eliminating dysfunctional thoughts and maladaptive behaviors.

cognitive enhancement Brain function enhancement by pharmacological, physiological, or surgical manipulation.

cognitive neuroscience Study of the neural bases of cognition.

cognitive therapy Psychotherapy based on the perspective that thoughts intervene between events and emotions, and thus the treatment of emotional disorders requires changing maladaptive patterns of thinking.

color constancy Phenomenon whereby an object’s perceived color tends to remain constant relative to other colors, regardless of changes in illumination.

coma Prolonged state of deep unconsciousness resembling sleep.

common ancestor Forebear of two or more lineages or family groups; ancestral to both groups.

compensation Following brain damage, neuroplastic ability to modify behavior from that used prior to the damage.

competitive inhibitor Drug, such as nalorphine and naloxone, that acts quickly to block opioid action by competing with the opioid for binding sites; used to treat opioid addiction.

computed tomography (CT) X-ray technique that produces a static three-dimensional image of the brain in cross section—a CT scan.

concentration gradient Difference in the relative abundance of a substance among regions of a container; allows the substance to diffuse from an area of higher concentration to an area of lower concentration.

conditioned response (CR) In Pavlovian conditioning, the learned response to a formerly neutral conditioned stimulus (CS).

conditioned stimulus (CS) In Pavlovian conditioning, an originally neutral stimulus that after association with an unconditioned stimulus (UCS) triggers a conditioned response (CR).

cone Photoreceptor specialized for color and high visual acuity.

connectome Comprehensive map of all structural connectivity (the physical wiring) in an organism’s nervous system.

consciousness The mind’s level of responsiveness to impressions made by the senses.

consolidation Process of stabilizing a memory trace after learning.

constraint-induced therapy Procedure in which restraint of a healthy limb forces a patient to use an impaired limb to enhance recovery of function.

contralateral neglect Ignoring a part of the body or world on the side opposite (contralateral to) that of a brain injury.

convergent thinking Form of thinking that searches for a single answer to a question (such as 2 + 2 = ?); contrasts with divergent thinking.

corpus callosum Band of white matter containing about 200 million nerve fibers that connects the two cerebral hemispheres to provide a route for direct communication between them.

cortical column Anatomic organization that represents a functional unit six cortical layers deep and approximately 0.5 mm square, perpendicular to the cortical surface.

corticospinal tract Bundle of nerve fibers directly connecting the cerebral cortex to the spinal cord, branching at the brainstem into an opposite-side lateral tract that informs movement of limbs and digits and a same side anterior tract that informs movement of the trunk; also called pyramidal tract.

cranial nerve One of a set of 12 nerve pairs that control sensory and motor functions of the head, neck, and internal organs.

critical period Developmental window during which some event has a long-lasting influence on the brain; also, sensitive period.

cross-tolerance Reduction of response to a novel drug because of tolerance to a chemically related drug.

culture Learned behaviors that are passed on from one generation to the next through teaching and imitation.

cytoarchitectonic map Map of the neocortex based on the organization, structure, and distribution of the cells.

D

deafferentation Loss of incoming sensory input, usually due to damage to sensory fibers; also loss of any afferent input to a structure.

decibel (dB) Measure of the relative physical intensity of sounds.

declarative memory Ability to recount what one knows, to detail the time, place, and circumstances of events; often lost in amnesia.

deep brain stimulation (DBS) Neurosurgery in which electrodes implanted in the brain stimulate a targeted area with a low-voltage electrical current to facilitate behavior.

delta (δ) rhythm Slow brain wave activity pattern associated with deep sleep.

dementia Acquired and persistent syndrome of intellectual impairment characterized by memory and other cognitive deficits and impairment in social and occupational functioning.

dendrite Branching extension of a neuron’s cell membrane; greatly increases the cell’s surface area; collects information from other cells.

dendritic spine Protrusion that greatly increases the dendrite’s surface area; typical point of dendritic contact with the axons of other cells.

depolarization Decrease in electrical charge across a membrane, usually due to the inward flow of sodium ions.

dermatome Body segment corresponding to a segment of the spinal cord.

Diagnostic and Statistical Manual of Mental Disorders (DSM) The American Psychiatric Association’s classification system for psychiatric disorders.

diaschisis Neural shock that follows brain damage in which areas connected to the site of damage show a temporary arrest of function.

dichotic listening Experimental procedure for simultaneously presenting a different auditory input to each ear through stereophonic earphones.

diencephalon The between brain, which integrates sensory and motor information on its way to the cerebral cortex.

diffusion Movement of ions from an area of higher concentration to an area of lower concentration through random motion.

diffusion tensor imaging (DTI) Magnetic resonance imaging method that can image fiber pathways in the brain by detecting the directional movements of water molecules.

dimer Two proteins combined into one.

disinhibition theory Explanation holding that alcohol has a selective depressant effect on the brain’s frontal cortex, which controls judgment, while sparing subcortical structures responsible for more instinctual behaviors, such as desire.

diurnal animal Organism that is active chiefly during daylight.

divergent thinking Form of thinking that searches for multiple solutions to a problem (how many ways can a pen be used?); contrasts with convergent thinking.

dopamine (DA) Amine neurotransmitter involved in coordinating movement, attention, learning, and in reinforcing behaviors.

dopamine hypothesis of schizophrenia Idea that excess dopamine activity causes symptoms of schizophrenia.

dorsal stream Visual processing pathway from V1 to the parietal lobe; guides movements relative to objects.

dorsolateral prefrontal cortex (DLPFC) Brodmann areas 9 and 46; makes reciprocal connections with posterior parietal cortex and the superior temporal sulcus; responsible for selecting behavior and movement with respect to temporal memory.

Down syndrome Chromosomal abnormality resulting in intellecutal impairment and other abnormalities, usually caused by an extra chromosome 21.

drug dependence insomnia Condition resulting from continuous use of sleeping pills; drug tolerance also results in deprivation of either REM or NREM sleep, leading the user to increase the drug dosage.

dualism Philosophical position that both a nonmaterial mind and a material body contribute to behavior.

dyslexia Impairment in learning to read and write; probably the most common learning disability.

E

echolocation Identifying and locating an object by bouncing sound waves off it.

efferent Conducting away from a CNS structure.

electrical stimulation Passage of an electrical current from the uninsulated tip of an electrode through tissue, resulting in changes in the electrical activity of the tissue.

electrical synapse See gap junction.

electrocorticography (ECoG) Graded potentials recorded with electrodes placed directly on the brain’s surface.

electroencephalogram (EEG) Graph that records electrical activity from the brain and mainly indicates graded potentials of many neurons.

electrographic seizures Abnormal rhythmic neuronal discharges; may be recorded by an electroencephalogram.

G-3

embodied behavior Theory that the movements we make and the movements we perceive in others are central to communication with others.

emotion Cognitive interpretation of subjective feelings.

emotional memory Memory for the affective properties of stimuli or events.

encephalization quotient (EQ) Jerison’s quantitative measure of brain size obtained from the ratio of actual brain size to expected brain size, according to the principle of proper mass, for an animal of a particular body size.

end plate On a muscle, the receptor–ion complex that is activated by the release of the neurotransmitter acetylcholine from the terminal of a motor neuron.

endocannabinoid Class of lipid neurotransmitters, including anandamide and 2-AG, synthesized at the postsynaptic membrane to act on receptors at the presynaptic membrane; affects appetite, pain, sleep, mood, memory, anxiety, and the stress response.

endorphin Opioid peptide that acts as a neurotransmitter and may be associated with feelings of pain or pleasure; mimicked by opioid drugs such as morphine, heroin, opium, and codeine.

enteric nervous system (ENS) Mesh of neurons embedded in the lining of the gut, running from the esophagus through the colon; controls the gut.

entorhinal cortex Located on the medial temporal lobe surface; provides a major route for neocortical input to the hippocampal formation; often degenerates in Alzheimer disease.

entrain Determine or modify the period of a biorhythm.

ependymal cell Glial cell that makes and secretes CSF; found on the walls of the brain’s ventricles.

epidermal growth factor (EGF) Neurotrophic factor; stimulates the subventricular zone to generate cells that migrate into the striatum and eventually differentiate into neurons and glia.

epigenetics Differences in gene expression related to environment and experience.

epinephrine (EP, or adrenaline) Chemical messenger that acts as a neurotransmitter in the CNS and as a hormone to mobilize the body for fight or flight during times of stress.

episodic memory Autobiographical memory for events pegged to specific place and time contexts.

estrogens Variety of sex hormones responsible for the distinguishing characteristics of the female.

event-related potentials (ERPs) Complex electroencephalographic waveform related in time to a specific sensory event.

evolutionary psychology Discipline that seeks to apply principles of natural selection to understand the causes of human behavior.

excitation Increase in the activity of a neuron or brain area.

excitatory postsynaptic potential (EPSP) Brief depolarization of a neuron membrane in response to stimulation, making the neuron more likely to produce an action potential.

explicit memory Conscious memory: subjects can retrieve an item and indicate that they know the retrieved item is the correct one.

extinction In neurology, neglect of information on one side of the body when presented simultaneously with similar information on the other side of the body.

extrastriate (secondary visual) cortex (V2–V5) Visual cortical areas in the occipital lobe outside the striate cortex.

eyeblink conditioning Experimental technique in which subjects learn to pair a formerly neutral stimulus with a defensive blinking response.

F

facial agnosia Face blindness—the inability to recognize faces; also called prosopagnosia.

fear conditioning Conditioned emotional response between a neutral stimulus and an unpleasant event, such as a shock, that results in a learned association.

festination Tendency to engage in a behavior, such as walking, faster and faster.

fetal alcohol spectrum disorder (FASD) Range of physical and intellectual impairments observed in some children born to alcoholic parents.

filopod (pl. filopodia) Process at the end of a developing axon that reaches out to search for a potential target or to sample the intercellular environment.

focal seizure Seizure that arises at a synchronous, hyperactive, localized brain region (at a focus).

forebrain Evolutionarily the newest part of the brain; coordinates advanced cognitive functions such as thinking, planning, and language; contains the limbic system, basal ganglia, and neocortex.

fovea Central region of the retina specialized for high visual acuity; its receptive fields are at the center of the eye’s visual field.

free-running rhythm Rhythm of the body’s own devising in the absence of all external cues.

frequency Number of cycles a wave completes in a given time.

frontal lobe Part of the cerebral cortex often generally characterized as performing the brain’s executive functions, such as decision making; lies anterior to the central sulcus and beneath the frontal bone of the skull.

functional magnetic resonance imaging (fMRI) Magnetic resonance imaging in which changes in elements such as iron or oxygen are measured during the performance of a specific behavior; used to measure cerebral blood flow during behavior or resting.

functional near-infrared spectroscopy (fNIRS) Noninvasive technique that gathers light transmitted through cortical tissue to image oxygen consumption; form of optical tomography.

G

G protein Guanyl nucleotide–binding protein coupled to a metabotropic receptor; when activated, binds to other proteins.

gamma-aminobutyric acid (GABA) Amino acid neurotransmitter; typically inhibits neurons.

ganglia Collection of nerve cells that function somewhat like a brain.

gap junction (electrical synapse) Area of contact between adjacent cells in which ion channels form a pore that allows ions to pass directly from one cell to the next.

gate Protein embedded in a cell membrane that allows substances to pass through the membrane on some occasions but not on others.

gender identity The degree to which a person feels male or female.

gene DNA segment that encodes the synthesis of a particular protein.

gene (DNA) methylation Epigenetic process in which a methyl group attaches to the DNA sequence, suppressing or enabling gene expression.

generalized anxiety disorder Persistently high levels of anxiety often accompanied by maladaptive behaviors to reduce anxiety; thought to be caused by chronic stress.

generalized seizure Seizure that may start at a focal location then spread rapidly and bilaterally to distributed networks in both hemispheres.

geniculostriate system Projections from the retina to the lateral geniculate nucleus to the visual cortex.

genotype Particular genetic makeup of an individual.

glabrous skin Skin that does not have hair follicles but contains larger numbers of sensory receptors than do hairy skin areas.

glial cell Nervous system cell that provides insulation, nutrients, and support and that aids in repairing neurons and eliminating waste products.

glioblast Product of a progenitor cell that gives rise to different types of glial cells.

glucocorticoid One of a group of steroid hormones, such as cortisol, secreted in times of stress; important in protein and carbohydrate metabolism.

glutamate (Glu) Amino acid neurotransmitter; typically excites neurons.

gonadal (sex) hormone One of a group of hormones, such as testosterone, that control reproductive functions and bestow sexual appearance and identity as male or female.

graded potential Small voltage fluctuation across the cell membrane.

gray matter Areas of the nervous system composed predominantly of cell bodies and capillary blood vessels that either collect and modify information or support this activity.

growth cone Growing tip of an axon.

growth spurt Sporadic period of sudden growth that lasts for a finite time.

gyrus (pl. gyri) A small protrusion or bump formed by the folding of the cerebral cortex.

H

habituation Learned behavior in which the response to a stimulus weakens with repeated presentations.

hair cell Specialized neurons in the cochlea tipped by cilia; when stimulated by waves in the cochlear fluid, the cilia bend and generate graded potentials in inner hair cells, the auditory receptor cells.

hapsis Perceptual ability to discriminate objects on the basis of touch.

hemisphere Literally, half a sphere, referring to one side of the cerebrum.

hertz (Hz) Measure of sound wave frequency (repetition rate); 1 hertz equals 1 cycle per second.

heterozygous Having two different alleles for the same trait.

hindbrain Evolutionarily the oldest part of the brain; contains the pons, medulla, reticular formation, and cerebellum, structures that coordinate and control most voluntary and involuntary movements.

hippocampus From the Greek word for seahorse; distinctive allocortical structure lying in the medial temporal lobe; participates in species-specific behaviors, memory, and spatial navigation and is vulnerable to the effects of stress.

histamine (H) Neurotransmitter that controls arousal and waking; can cause the constriction of smooth muscles; when activated in allergic reactions, constricts airway and contributes to asthma.

homeostatic hormone One of a group of hormones that maintain internal metabolic balance and regulate physiological systems in an organism.

homeostatic mechanism Process that maintains critical body functions within a narrow, fixed range.

hominid General term referring to primates that walk upright, including all forms of humans, living and extinct.

homonymous hemianopia Blindness of an entire left or right visual field.

homozygous Having two identical alleles for a trait.

homunculus Representation of the human body in the sensory or motor cortex; also any topographical representation of the body by a neural area.

HPA axis Hypothalamic–pituitary–adrenal circuit that controls the production and release of hormones related to stress.

Huntington disease Hereditary disease characterized by chorea (ceaseless involuntary jerky movements) and progressive dementia, ending in death.

hydrocephalus Buildup of fluid pressure in the brain and, in infants, swelling of the head, if the flow of CSF is blocked; can result in intellectual impairment.

hydrogen sulfide (H₂S) Gaseous neurotransmitter; slows cellular metabolism.

hyperconnectivity Increased local connections between two related brain regions.

hyperkinetic symptom Excessive involuntary movement, as seen in Tourette syndrome.

G-4

hyperphagia Overeating that leads to significant weight gain.

hyperpolarization Increase in electrical charge across a membrane, usually due to the inward flow of chloride or sodium ions or the outward flow of potassium ions.

hypnogogic hallucination Dreamlike event as sleep begins or while a person is in a state of cataplexy.

hypokinesia Slowness or absence of movement.

hypokinetic symptom Paucity of movement, as seen in Parkinson disease.

hypothalamus Diencephalon structure that contains many nuclei associated with temperature regulation, eating, drinking, and sexual behavior.

hypovolemic thirst Thirst produced by a loss of overall fluid volume from the body.

I

implicit memory Unconscious memory: subjects can demonstrate knowledge, such as a skill, conditioned response, or recall of events on prompting but cannot explicitly retrieve the information.

imprinting Formation of an attachment by an animal to one or more objects or animals at a critical period in development.

inhibition Decrease in the activity of a neuron or brain area.

inhibitory postsynaptic potential (IPSP) Brief hyperpolarization of a neuron membrane in response to stimulation, making the neuron less likely to produce an action potential.

initial segment Area near or overlapping the axon hillock where the action potential begins.

innate releasing mechanism (IRM) Hypothetical mechanism that detects specific sensory stimuli and directs an organism to take a particular action.

insomnia Disorder of slow-wave sleep resulting in prolonged inability to sleep.

insula Multifunctional cortical tissue located within the lateral fissure; contains language and taste perception–related regions and neural structures underlying social cognition.

intelligence A Hebb’s term for innate intellectual potential, which is highly heritable and cannot be measured directly.

intelligence B Hebb’s term for observed intelligence, influenced by experience and other factors in the course of development; measured by intelligence tests.

interneuron Association cell interposed between a sensory neuron and a motor neuron; in mammals, interneurons constitute most of the brain’s neurons.

ionotropic receptor Embedded membrane protein; acts as (1) a binding site for a neurotransmitter and (2) a pore that regulates ion flow to directly and rapidly change membrane voltage.

ischemia Lack of blood to the brain, usually as a result of a stroke.

J

jet lag Fatigue and disorientation resulting from rapid travel through time zones and exposure to a changed light–dark cycle.

K

Klüver-Bucy syndrome Behavioral syndrome, characterized especially by hypersexuality, that results from bilateral injury to the temporal lobe.

Korsakoff syndrome Permanent loss of the ability to learn new information (anterograde amnesia) and to retrieve old information (retrograde amnesia) caused by diencephalic damage resulting from chronic alcoholism or malnutrition that produces a vitamin B₁ deficiency.

L

lateralization Localization of function primarily on one side of the brain.

law of Bell and Magendie The principle that sensory fibers are dorsal and motor fibers are ventral.

learned taste aversion Acquired association between a specific taste or odor and illness; leads to an aversion to foods that have the taste or odor.

learning Relatively permanent change in behavior that results from experience.

learning set Rules of the game; implicit understanding of how a problem can be solved with a rule that can be applied in many different situations.

Lewy body Circular fibrous structure found in several neurodegenerative disorders; forms within the cytoplasm of neurons and is thought to result from abnormal neurofilament metabolism.

light pollution Exposure to artificial light that changes activity patterns and so disrupts circadian rhythms.

limbic system Disparate forebrain structures lying between the neocortex and the brainstem that form a functional system controlling affective and motivated behaviors and certain forms of memory; includes cingulate cortex, amygdala, and hippocampus, among other structures.

locked-in syndrome Condition in which a patient is aware and awake but cannot move or communicate verbally because of complete paralysis of nearly all voluntary muscles except the eyes.

long-term depression (LTD) Long-lasting decrease in synaptic effectiveness after low-frequency electrical stimulation.

long-term potentiation (LTP) Long-lasting increase in synaptic effectiveness after high-frequency stimulation.

luminance contrast Amount of light an object reflects relative to its surroundings.

M

magnetic resonance imaging (MRI) Technique that produces a static three-dimensional brain image by passing a strong magnetic field through the brain, followed by a radio wave, then measuring a radio frequency signal emitted from hydrogen atoms.

magnetic resonance spectroscopy (MRS) Magnetic resonance imaging method that uses the hydrogen proton signal to determine the concentration of brain metabolites.

magnetoencephalogram (MEG) Magnetic potentials recorded from detectors placed outside the skull.

magnocellular (M) cell Large visual system neuron sensitive to moving stimuli and black-white vision.

major depression Mood disorder characterized by prolonged feelings of worthlessness and guilt, disruption of normal eating habits, sleep disturbances, a general slowing of behavior, and frequent thoughts of suicide.

mania Disordered mental state of extreme excitement.

masculinization Process by which exposure to androgens (male sex hormones) alters the brain, rendering it identifiably male.

materialism Philosophical position that behavior can be explained as a function of the nervous system without recourse to the mind.

medial forebrain bundle (MFB) Tract that connects brainstem structures with various parts of the limbic system; forms the activating projections that run from the brainstem to basal ganglia and frontal cortex.

medial geniculate nucleus Major thalamic region concerned with audition.

medial pontine reticular formation (MPRF) Nucleus in the pons participating in REM sleep.

melatonin Hormone secreted by the pineal gland during the dark phase of the day–night cycle; influences daily and seasonal biorhythms.

meme An idea, behavior, or style that spreads from person to person within a culture.

memory Ability to recall or recognize previous experience.

Ménière disease Disorder of the middle ear resulting in vertigo and loss of balance.

meninges Three layers of protective tissue—dura mater, arachnoid, and pia mater—that encase the brain and spinal cord.

mentalism Explanation of behavior as a function of the nonmaterial mind.

metabolic syndrome Combinations of medical disorders, including obesity and insulin abnormalities, that collectively increase the risk of developing cardiovascular disease and diabetes.

metabotropic receptor Embedded membrane protein with a binding site for a neurotransmitter linked to a G protein; can affect other receptors or act with second messengers to affect other cellular processes, including opening a pore.

metaplasticity Interaction among different plastic changes in the brain.

microdialysis Technique used to determine the chemical constituents of extracellular fluid in freely moving animals.

microelectrode A microscopic insulated wire or a saltwater-filled glass tube whose uninsulated tip is used to stimulate or record from neurons.

microglia Glial cells that originate in the blood, aid in cell repair, and scavenge debris in the nervous system.

microsleep Brief sleep period lasting a second or so.

midbrain Central part of the brain; contains neural circuits for hearing and seeing as well as orienting movements.

mind Proposed nonmaterial entity responsible for intelligence, attention, awareness, and consciousness.

mind–body problem Difficulty of explaining how a nonmaterial mind and a material body interact.

minimally conscious state (MCS) Condition in which a person can display some rudimentary behaviors, such as smiling or uttering a few words, but is otherwise not conscious.

mirror neuron Cell in the primate premotor and parietal cortex that fires when an individual observes an action taken by another individual.

monoamine oxidase (MAO) inhibitor Antidepressant drug that blocks the enzyme monoamine oxidase from degrading such neurotransmitters as DA, NE, and 5-HT.

monosynaptic reflex Reflex requiring one synapse between sensory input and movement.

mood stabilizer Drug for treating bipolar disorder; mutes the intensity of one pole of the disorder, thus making the other pole less likely to recur.

motivation Behavior that seems purposeful and goal-directed.

motor neuron Cell that carries efferent information from the brain and spinal cord to make muscles contract.

motor sequence Movement modules preprogrammed by the brain and produced as a unit.

multiple sclerosis (MS) Nervous system disorder resulting from the loss of myelin around axons in the CNS.

mutation Alteration of an allele that yields a different version of its protein.

myelin Glial coating that surrounds axons in the central and peripheral nervous systems; prevents adjacent neurons from short circuiting.

N

narcolepsy Slow-wave sleep disorder in which a person uncontrollably falls asleep at inappropriate times.

natural selection Darwin’s theory for explaining how new species evolve and how existing species change over time. Differential success in the reproduction of different characteristics (phenotypes) results from the interaction of organisms with their environment.

neocortex (cerebral cortex) Most recently evolved outer layer (new bark) of the forebrain, composed of about six layers of gray matter; constructs our reality.

neoteny Process in which juvenile stages of predecessors become adult features of descendants; idea derived from the observation that more recently evolved species resemble the young of their common ancestors.

nerve Large collection of axons coursing together outside the CNS.

nerve growth factor (NGF) Neurotrophic factor that stimulates neurons to grow dendrites and synapses and in some cases promotes the survival of neurons.

G-5

nerve impulse Propagation of an action potential on the membrane of an axon.

nerve net Simple nervous system that has no center but consists of neurons that receive sensory information and connect directly to other neurons that move muscles.

netrin Member of the only class of tropic molecules yet isolated.

neural Darwinism Hypothesis that the processes of cell death and synaptic pruning are, like natural selection in species, the outcome of competition among neurons for connections and metabolic resources in a neural environment.

neural network Functional group of neurons that connects wide areas of the brain and spinal cord.

neural plate Primitive neural tissue that gives rise to the neural tube.

neural stem cell Self-renewing multipotential cell that gives rise to any of the different types of neurons and glia in the nervous system.

neural tube Structure in the early stage of brain development from which the brain and spinal cord develop.

neuritic plaque Area of incomplete necrosis (dead tissue) consisting of a central protein core (amyloid) surrounded by degenerative cellular fragments; often seen in the cortex of people with dementias such as Alzheimer disease.

neuroblast Product of a progenitor cell that gives rise to any of the different types of neurons.

neuroeconomics Interdisciplinary field that seeks to understand how the brain makes decisions.

neuron Specialized nerve cell engaged in information processing.

neuropeptide Short (fewer than 100), multifunctional amino acid chain; acts as a neurotransmitter and can act as a hormone; may contribute to learning.

neuroplasticity The nervous system’s potential for physical or chemical change to adapt to environmental change and to compensate for injury.

neuroprosthetics Field that develops computer-assisted devices to replace lost biological function.

neuroprotectant Drug used to try to block the cascade of poststroke neural events.

neuropsychoanalysis Movement within neuroscience and psychoanalysis to combine the insights of both to yield a unified understanding of mind and brain.

neuropsychology Study of the relations between brain function and behavior, especially in humans.

neurotransmitter Chemical with an excitatory or inhibitory effect when released by a neuron onto a target.

neurotrophic factor A chemical compound that supports growth and differentiation in developing neurons and may act to keep certain neurons alive in adulthood.

nitric oxide (NO) Gaseous neurotransmitter; acts, for example, to dilate blood vessels, aid digestion, and activate cellular metabolism.

nocioception Perception of pain, temperature, and itch.

node of Ranvier The part of an axon that is not covered by myelin.

nonregulatory behavior Behavior unnecessary to the animal’s basic survival needs.

noradrenergic neuron From adrenaline, Latin for epinephrine; a neuron containing norepinephrine.

norepinephrine (NE, or noradrenaline) Neurotransmitter that accelerates heart rate in mammals; found in the brain and in the sympathetic division of the ANS.

NREM (non-REM) sleep Slow-wave sleep associated with delta rhythms.

nuclei (sing. nucleus) A group of cells forming a cluster that can be identified with special stains to form a functional grouping.

O

obesity Excessive accumulation of body fat.

obsessive-compulsive disorder (OCD) Behavior characterized by compulsively repeated acts (such as hand washing) and repetitive, often unpleasant, thoughts (obsessions).

occipital lobe Part of the cerebral cortex where visual processing begins; lies at the back of the brain and beneath the occipital bone.

ocular dominance column Functional column in the visual cortex maximally responsive to information coming from one eye.

oligodendroglia Glial cells in the CNS that myelinate axons.

operant conditioning Learning procedure in which the consequences (such as obtaining a reward) of a particular behavior (such as pressing a bar) increase or decrease the probability of the behavior occurring again; also called instrumental conditioning.

opioid analgesic Drug such as morphine, with sleep-inducing (narcotic) and pain-relieving (analgesic) properties; originally called narcotic analgesic.

opponent process Explanation of color vision that emphasizes the importance of the apparently opposing color pairs: red versus green and blue versus yellow.

optic ataxia Deficit in the visual control of reaching and other movements.

optic chiasm Junction of the optic nerves, one from each eye, at which the axons from the nasal halves of the retinas cross to the brain’s opposite side.

optic flow Streaming of visual stimuli that accompanies an observer’s movement through space.

optogenetics Transgenic technique that combines genetics and light to excite or inhibit targeted cells in living tissue.

orbitofrontal cortex (OFC) Prefrontal cortex behind the eye sockets (the orbits); receives projections from the dorsomedial nucleus of the thalamus; central to a variety of emotional and social behaviors, including eating; also called orbital frontal cortex.

organizational hypothesis Proposal that hormonal action during development alters tissue differentiation; for example, testosterone masculinizes the brain.

orienting movement Movement related to sensory inputs, such as turning the head to see the source of a sound.

oscilloscope Device that serves as a sensitive voltmeter by registering changes in voltage over time.

osmotic thirst Thirst that results from a high concentration of dissolved chemicals, or solutes, in body fluids.

ossicle Bone of the middle ear; includes malleus (hammer), incus (anvil), and stapes (stirrup).

otoacousitic emissions Spontaneous or evoked sound waves produced within the ear by the cochlea and escape from the ear.

P

pain gate Hypothetical neural circuit in which activity in fine-touch and pressure pathways diminishes the activity in pain and temperature pathways.

panic disorder Recurrent attacks of intense terror that come on without warning and without any apparent relation to external circumstances.

parahippocampal cortex Cortex located along the dorsal medial temporal lobe surface.

paralysis Loss of sensation and movement due to nervous system injury.

paraplegia Paralysis of the legs due to spinal cord injury.

parasympathetic division Part of the autonomic nervous system; acts in opposition to the sympathetic division—for example, preparing the body to rest and digest by reversing the alarm response or stimulating digestion.

parietal lobe Part of the cerebral cortex that directs movements toward a goal or to perform a task, such as grasping an object; lies posterior to the central sulcus and beneath the parietal bone at the top of the skull.

Parkinson disease Disorder of the motor system correlated with a loss of dopamine from the substantia nigra and characterized by tremors, muscular rigidity, and a reduction in voluntary movement.

parvocellular (P) cell Small visual system neuron sensitive to differences in form and color.

Pavlovian conditioning Learning achieved when neutral stimulus (such as a tone) comes to elicit a response after its repeated pairing with some event (such as delivery of food); also called classical conditioning or respondent conditioning.

peptide hormone Chemical messenger synthesized by cellular DNA that acts to affect the target cell’s physiology.

perception Subjective interpretation of sensations by the brain.

periaqueductal gray matter (PAG) Nuclei in the midbrain that surround the cerebral aqueduct joining the third and fourth ventricles; PAG neurons contain circuits for species-typical behaviors (e.g., female sexual behavior) and play an important role in the modulation of pain.

peribrachial area Cholinergic nucleus in the dorsal brainstem having a role in REM sleep behaviors; projects to medial pontine reticular formation.

period Time required to complete an activity cycle.

peripheral nervous system (PNS) All of the neurons in the body outside the brain and spinal cord; provides sensory and motor connections to and from the central nervous system.

perirhinal cortex Cortex lying next to the rhinal fissure on the ventral surface of the brain.

perseveration Tendency to emit repeatedly the same verbal or motor response to varied stimuli.

persistent vegetative state (PVS) Condition in which a person is alive but unaware, unable to communicate or to function independently at even the most basic level.

phenotype Set of individual characteristics that can be seen or measured.

phenotypic plasticity An individual’s capacity to develop into more than one phenotype.

phenylketonuria (PKU) Behavioral disorder caused by elevated levels of the amino acid phenylalanine in the blood and resulting from a defect in the gene for the enzyme phenylalanine hydroxylase; the major symptom is severe developmental disability.

pheromone Odorant biochemical released by one animal that acts as a chemosignal and can affect the physiology or behavior of another animal.

phobia Fear of a clearly defined object or situation.

photoreceptor Specialized retinal neuron that transduces light into neural activity.

pituitary gland Endocrine gland attached to the bottom of the hypothalamus; its secretions control the activities of many other endocrine glands; associated with biological rhythms.

place cell Hippocampal neuron maximally responsive to specific locations in the world.

plasticity The nervous system’s potential for physical or chemical change; enhances its adaptability to environmental change and its ability to compensate for injury. (Also called neuroplasticity.)

positron emission tomography (PET) Imaging technique that detects changes in blood flow by measuring changes in the uptake of compounds such as oxygen or glucose; used to analyze the metabolic activity of neurons.

posterior spinothalamic tract Pathway that carries fine-touch and pressure fibers.

postsynaptic membrane Membrane on the transmitter, or input, side of a synapse.

posttraumatic stress disorder (PTSD) Syndrome characterized by physiological arousal associated with recurrent memories and dreams arising from a traumatic event that occurred months or years earlier.

prefrontal cortex (PFC) Extensive frontal lobe area anterior to the motor and premotor cortex; key to controlling executive functions such as planning.

preparedness Predisposition to respond to certain stimuli differently from other stimuli.

presynaptic membrane Axon terminal membrane on the transmitter, or output, side of a synapse.

primary auditory cortex (area A1) Asymmetrical structures within Heschl’s gyrus in the temporal lobes; receive input from the ventral region of the medial geniculate nucleus.

G-6

primary visual cortex (V1) Striate cortex in the occipital lobe that receives input from the lateral geniculate nucleus.

priming Using a stimulus to sensitize the nervous system to a later presentation of the same or a similar stimulus.

prion From protein and infection, an abnormally folded protein that causes progressive neurodegenerative disorders.

procedural memory Ability to recall a movement sequence or how to perform some act or behavior.

progenitor cell (precursor cell) Derived from a stem cell; it migrates and produces a neuron or a glial cell.

proprioception Perception of the position and movement of the body, limbs, and head.

prosody Melodic tone of the speaking voice.

protein Folded-up polypeptide chain that serves a particular function in the body.

psyche Synonym for mind, an entity once proposed to be the source of human behavior.

psychedelic drug Drug that can alter sensation and perception; examples are lysergic acid diethylamide (LSD), mescaline, and psilocybin.

psychoactive drug Substance that acts to alter mood, thought, or behavior; is used to manage neuropsychological illness; or is abused.

psychological construct Idea or set of impressions that some mental ability exists as an entity; memory, language, and emotion are examples.

psychomotor activation Increased behavioral and cognitive activity: at certain levels of consumption, the drug user feels energetic and in control.

psychopharmacology Study of how drugs affect the nervous system and behavior.

psychosurgery Any neurosurgical technique intended to alter behavior.

psychotherapy Talk therapy derived from Freudian psychoanalysis and other psychological interventions.

pump Protein in the cell membrane that actively transports a substance across the membrane.

Purkinje cell Distinctively shaped interneuron found in the cerebellum.

pyramidal cell Distinctively shaped interneuron found in the cerebral cortex.

Q

quadrantanopia Blindness of one quadrant of the visual field.

quadriplegia Paralysis of the legs and arms due to spinal cord injury.

quantum (pl. quanta) Amount of neurotransmitter, equivalent to the content of a single synaptic vesicle, that produces a just-observable change in postsynaptic electric potential.

R

radial glial cell Path-making cell that a migrating neuron follows to its appropriate destination.

rapidly adapting receptor Body sensory receptor that responds briefly to the onset of a stimulus on the body.

rate-limiting factor Any chemical in limited supply that restricts the pace at which another chemical can be synthesized.

real-time fMRI (rt-fMRI) Behavior-modification technique in which individuals learn to change their behavior by controlling their own patterns of brain activation.

receptive field Sensory region that stimulates a receptor cell or neuron.

reconsolidation Process of restabilizing a memory trace after the memory is revisited.

referred pain Pain that arises in one of the internal organs but is felt on the surface of the body.

regulatory behavior Behavior motivated to meet the animal’s survival needs.

reinforcer In operant conditioning, any event that strengthens the behavior it follows.

relatively refractory The state of an axon in the later phase of an action potential during which increased electrical current is required to produce another action potential; a phase during which potassium channels are still open.

releasing hormone Peptide released by the hypothalamus that increases or decreases hormone release from the anterior pituitary.

REM sleep Fast brain wave pattern displayed by the neocortical EEG record during sleep.

resting potential Electrical charge across the insulating cell membrane in the absence of stimulation; a store of potential energy produced by a greater negative charge on the intracellular side relative to the extracellular side.

resting-state fMRI (rs-fMRI) Magnetic resonance imaging method that measures changes in elements such as iron or oxygen when the individual is resting (not engaged in a specific task).

reticular activating system (RAS) Large reticulum (mixture of cell nuclei and nerve fibers) that runs through the center of the brainstem; associated with sleep–wake behavior and behavioral arousal; also called the reticular formation.

reticular formation Midbrain area in which nuclei and fiber pathways are mixed, producing a netlike appearance; associated with sleep–wake behavior and behavioral arousal.

retina Light-sensitive surface at the back of the eye consisting of neurons and photoreceptor cells.

retinal ganglion cell (RGC) One of a group of retinal neurons with axons that give rise to the optic nerve.

retinohypothalamic tract Neural route formed by axons of photosensitive retinal ganglion cells (pRGCs) from the retina to the suprachiasmatic nucleus; allows light to entrain the SCN’s rhythmic activity.

retrograde amnesia Inability to remember events that took place before the onset of amnesia.

reuptake Deactivation of a neurotransmitter when membrane transporter proteins bring the transmitter back into the presynaptic axon terminal for reuse.

rod Photoreceptor specialized for functioning at low light levels.

S

saltatory conduction Fast propagation of an action potential at successive nodes of Ranvier; saltatory means leaping.

schizophrenia Behavioral disorder characterized by delusions, hallucinations, disorganized speech, blunted emotion, agitation or immobility, and a host of associated symptoms.

Schwann cell Glial cell in the PNS that myelinates sensory and motor axons.

scotoma Small blind spot in the visual field caused by migraine or by a small lesion of the visual cortex.

scratch reflex Automatic response in which an animal’s hind limb reaches to remove a stimulus from the surface of its body.

second-generation antidepressant Drug that acts similarly to tricyclics (first-generation antidepressants) but more selectively on 5-HT reuptake transporter proteins; also called atypical antidepressant.

second messenger Chemical that initiates a biochemical process when activated by a neurotransmitter (the first messenger).

segmentation Division into a number of parts that are similar; refers to the idea that many animals, including vertebrates, are composed of similarly organized body segments.

selective serotonin reuptake inhibitor (SSRI) Tricyclic antidepressant drug that blocks 5-HT reuptake into the presynaptic terminal.

sensation Registration by the sensory organs of physical stimuli from the environment.

sensitization Learned behavior in which the response to a stimulus strengthens with repeated presentations.

sensory deprivation Experimental setup in which a participant is allowed only restricted sensory input; participants generally have a low tolerance for deprivation and may even hallucinate.

sensory neuron Cell that detects or carries sensory information into the spinal cord and brain.

serotonin (5-HT) Amine neurotransmitter; helps to regulate mood and aggression, appetite and arousal, perception of pain, and respiration.

sexual dimorphism Differential development of brain areas in the two sexes.

sexual orientation A person’s pattern of sexual attraction—to the opposite sex or to the same sex or to both sexes.

sleep apnea Inability to breathe during sleep, causing a sleeper to wake up to breathe.

sleep paralysis Atonia and dreaming occurring when a person is awake, usually just falling asleep or waking up.

slow-wave sleep NREM sleep.

slowly adapting receptor Body sensory receptor that responds as long as a sensory stimulus is on the body.

small-molecule transmitter Quick-acting neurotransmitter synthesized in the axon terminal from products derived from the diet.

social neuroscience Interdisciplinary field that seeks to understand how the brain mediates social interactions.

somatic marker hypothesis Proposal that marker signals arising from emotions and feelings act to guide behavior and decision making, usually in an unconscious process.

somatic nervous system (SNS) Part of the PNS that includes the cranial and spinal nerves to and from the muscles, joints, and skin, which produce movement, transmit incoming sensory input, and inform the CNS about the position and movement of body parts.

somatosensory neuron Brain cell that brings sensory information from the body into the spinal cord.

sound wave Mechanical displacement of molecules caused by changing pressure that possesses the physical properties of frequency, amplitude, and complexity. Also compression wave.

spatial summation Addition of one graded potential to another that occur close in space.

species Group of organisms that can interbreed.

species-typical behavior Behavior that is characteristic of all members of a species, such as walking in amphibians.

spinal cord Part of the central nervous system encased within the vertebrae (spinal column); provides most of the connections between the brain and the rest of the body.

split brain Surgical disconnection of the hemispheres by severing the corpus callosum.

stereotaxic apparatus Surgical instrument that permits the researcher to target a specific part of the brain.

steroid hormone Fat-soluble chemical messenger synthesized from cholesterol.

storage granule Membranous compartment that holds several vesicles containing a neurotransmitter.

stretch-sensitive channel Ion channel on a tactile sensory neuron that activates in response to stretching of the membrane, initiating a nerve impulse.

striate cortex Primary visual cortex (V1) in the occipital lobe; shows stripes (striations) on staining.

striatum Caudate nucleus and putamen of the basal ganglia.

stroke Sudden appearance of neurological symptoms as a result of severely interrupted blood flow.

substance abuse A pattern of drug use in which people rely on a drug chronically and excessively, allowing it to occupy a central place in their life.

subunit Protein molecule that assembles with other protein molecules.

subventricular zone Lining of neural stem cells surrounding the ventricles in adults.

G-7

sudden infant death syndrome (SIDS) Unexplained death while asleep of a seemingly healthy infant less than 1 year old.

sulcus (pl. sulci) A groove in brain matter; most are in the neocortex or cerebellum.

supplementary speech area Speech production region on the left frontal lobe dorsal surface.

suprachiasmatic nucleus (SCN) Master biological clock located in the hypothalamus just above the optic chiasm.

sympathetic division Part of the autonomic nervous system; arouses the body for action, such as mediating the involuntary fight-or-flight response to alarm by increasing heart rate and blood pressure.

symptomatic seizure Identified with a specific cause, such as infection, trauma, tumor, vascular malformation, toxic chemicals, very high fever, or other neurological disorders.

synapse Spatial junction between one neuron and another; forms the information transfer site between neurons.

synaptic cleft Gap separating the neuronal presynaptic membrane from the postsynaptic membrane.

synaptic vesicle Membranous compartment that encloses a quantum of neurotransmitter.

synesthesia Ability to perceive a stimulus of one sense as the sensation of a different sense, as when sound produces a sensation of color; literally, feeling together.

syntax Ways in which words are put together; proposed to be unique to human language.

synthetic biology Design and construction of biological devices, systems, and machines not found in nature.

T

tardive dyskinesia Inability to stop the tongue or other body parts from moving; motor side effect of neuroleptic drugs.

Tay-Sachs disease Inherited birth defect caused by the loss of genes that encode the enzyme necessary for breaking down certain fatty substances; appears 4 to 6 months after birth and results in intellectual disability, physical changes, and death by about age 5.

tectopulvinar system Projections from the retina to the superior colliculus to the pulvinar (thalamus) to the parietal and temporal visual areas.

tectum Roof (area above the ventricle) of the midbrain; its functions are sensory processing, particularly visual and auditory, and the production of orienting movements.

tegmentum Floor (area below the ventricle) of the midbrain; a collection of nuclei with movement-related, species-specific, and pain perception functions.

temporal lobe Part of the cerebral cortex that functions in connection with hearing, language, and musical abilities; lies below the lateral fissure, beneath the temporal bone at the side of the skull.

temporal summation Addition of one graded potential to another that occur close in time.

terminal button (end foot) Knob at the tip of an axon that conveys information to other neurons.

testosterone Sex hormone secreted by the testes and responsible for the distinguishing characteristics of the male.

thalamus Diencephalon structure through which information from all sensory systems is integrated and projected into the appropriate region of the neocortex.

theory of mind Ability to attribute mental states to others.

threshold potential Voltage on a neural membrane at which an action potential is triggered by the opening of sodium and potassium voltage-sensitive channels; about -50 mV relative to extracellular surround. Also called threshold limit.

tolerance Decrease in response to a drug with the passage of time.

tonotopic representation In audition, structural organization for processing of sound waves from lower to higher frequencies.

topographic map Spatially organized neural representation of the external world.

topographic organization Neural spatial representation of the body or areas of the sensory world perceived by a sensory organ.

Tourette syndrome Disorder of the basal ganglia characterized by tics, involuntary vocalizations (including curse words and animal sounds), and odd, involuntary movements of the body, especially of the face and head.

tract Large collection of axons coursing together in the CNS.

transcranial magnetic stimulation (TMS) Procedure in which a magnetic coil is placed over the skull to stimulate the underlying brain; used either to induce behavior or to disrupt ongoing behavior.

transgender Possessing personal characteristics that transcend traditional gender boundaries and corresponding sexual norms; a person’s belief that he or she was born the wrong sex.

transgenic animal Product of technology in which one or more genes from one species is introduced into the genome of another species to be passed along and expressed in subsequent generations.

transmitter-activated receptor Protein that has a binding site for a specific neurotransmitter and is embedded in the membrane of a cell.

transmitter-sensitive channel Receptor complex that has both a receptor site for a chemical and a pore through which ions can flow.

transporter Protein molecule that pumps substances across a membrane.

traumatic brain injury (TBI) Wound to the brain that results from a blow to the head.

trichromatic theory Explanation of color vision based on the coding of three primary colors: red, green, and blue.

tricyclic antidepressant First-generation antidepressant; its chemical structure, characterized by three rings, blocks 5-HT reuptake transporter proteins.

tropic molecule Signaling molecule that attracts or repels growth cones.

tumor Mass of new tissue that grows uncontrolled and independent of surrounding structures.

U

unconditioned response (UCR) Unlearned, naturally occurring response to the unconditioned stimulus (UCS), such as salivation when food is in the mouth.

unconditioned stimulus (UCS) A stimulus that naturally and automatically (unconditionally) triggers an unconditioned response (UCR).

V

ventral stream Visual processing pathway from V1 to the temporal lobe for object identification and perceiving related movements.

ventricle One of four cavities in the brain that contain CSF to cushion the brain; may play a role in maintaining brain metabolism.

ventrolateral thalamus Part of the thalamus that carries information about body senses to the somatosensory cortex.

vertebrae (sing. vertebra) The bones that form the spinal column.

vestibular system Somatosensory system comprising a set of receptors in each inner ear that respond to body position and to movement of the head.

virtual-reality (VR) exposure therapy Controlled virtual immersion environment that, by allowing individuals to relive traumatic events, gradually desensitizes them to stress.

visual field Region of the visual world seen by the eyes.

visual-form agnosia Inability to recognize objects or drawings of objects.

visuospatial memory Use of visual information to recall an object’s location in space.

voltage gradient Difference in charge between two regions that allows a flow of current if the two regions are connected.

voltage-sensitive channel Gated protein channel that opens or closes only at specific membrane voltages.

voltmeter Device that measures the flow and the strength of electrical voltage by recording the difference in electrical potential between two bodies.

W

wanting-and-liking theory Explanation holding that when a drug is associated with certain cues, the cues themselves elicit desire for the drug; also called incentive sensitization theory.

Wernicke’s area Secondary auditory cortex (planum temporale) lying behind Heschl’s gyrus at the rear of the left temporal lobe; regulates language comprehension. Also posterior speech zone.

white matter Areas of the nervous system rich in fat-sheathed neural axons that form the connections between brain cells.

wild type Typical allele (most common in a population).

withdrawal symptom Physical and psychological behavior displayed by an addict when drug use ends.

Z

Zeitgeber Environmental event that entrains biological rhythms: German for time giver.