Darwin argued that natural selection shapes behaviors as well as bodies.

The principle that the inherited traits enabling an organism to survive and reproduce in a particular environment will (in competition with other trait variations) most likely be passed on to succeeding generations.

The study of the evolution of behavior and the mind, using principles of natural selection.

The study of the relative power and limits of genetic and environmental influences on behavior.

A random error in gene replication that leads to a change.

Every nongenetic influence, from prenatal nutrition to our experiences of the people and things around us.

The genetic transfer of characteristics from parents to offspring.

The biochemical units of heredity.

The complete instructions for making an organism.

Individuals who developed from a single fertilized egg that split in two, creating two genetically identical organisms.

Individuals who developed from separate fertilized eggs. They are genetically no closer than ordinary siblings, but they shared a prenatal environment

The interplay that occurs when the effect of one factor (such as environment) depends on another factor (such as heredity)

“Above” or “in addition to” (epi) genetics; the study of the molecular mechanisms by which environments can influence genetic expression (without a DNA change).

The body’s speedy, electrochemical communication network, consisting of all the nerve cells of the peripheral and central nervous systems.

The brain and spinal cord.

The sensory and motor neurons that connect the central nervous system (CNS) to the rest of the body.

Bundled axons that form neural cables connecting the central nervous system with muscles, glands, and sensory organs.

Neurons that carry incoming information from the body’s tissues and sensory receptors to the brain and spinal cord.

Neurons that carry outgoing information from the brain and spinal cord to the muscles and glands.

Neurons within the brain and spinal cord; they communicate internally and process information between the sensory inputs and motor outputs

The division of the peripheral nervous system that controls the body’s skeletal muscles. Also called the skeletal nervous system.

The part of the peripheral nervous system that controls the glands and the muscles of the internal organs (such as the heart). Its sympathetic division arouses; its parasympathetic division calms.

The division of the autonomic nervous system that arouses the body, mobilizing its energy.

The division of the autonomic nervous system that calms the body, conserving its energy.

A simple, automatic response to a sensory stimulus, such as the knee-jerk reflex.

A nerve cell; the basic building block of the nervous system.

The part of a neuron that contains the nucleus; the cell’s life-support center.

A neuron’s often bushy, branching extensions that receive and integrate messages, conducting impulses toward the cell body.

The segmented neuron extension that passes messages through its branches to other neurons or to muscles or glands.

A fatty tissue layer segmentally encasing the axons of some neurons; it enables vastly greater transmission speed as neural impulses hop from one node to the next.

Cells in the nervous system that support, nourish, and protect neurons; they may also play a role in learning, thinking, and memory.

A neural impulse; a brief electrical charge that travels down an axon.

The level of stimulation required to trigger a neural impulse.

In neural processing, a brief resting pause that occurs after a neuron has fired; subsequent action potentials cannot occur until the axon returns to its resting state.

A neuron’s reaction of either firing (with a full-strength response) or not firing.

The junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron. The tiny gap at this junction is called the synaptic gap or synaptic cleft.

Chemical messengers that cross the synaptic gap between neurons. When released by the sending neuron, neurotransmitters travel across the synapse and bind to receptor sites on the receiving neuron, thereby influencing whether that neuron will generate a neural impulse.

A neurotransmitter’s reabsorption by the sending neuron.

“Morphine within”; natural, opioid-like neurotransmitters linked to pain control and to pleasure.

A molecule that increases a neurotransmitter’s action.

A molecule that inhibits or blocks a neurotransmitter’s action.

The body’s “slow” chemical communication system; a set of glands and fat tissue that secrete hormones into the bloodstream.

Chemical messengers that are manufactured by the endocrine glands, travel through the bloodstream, and affect other tissues.

A chemical substance that alters the brain, causing changes in perceptions and moods.

A disorder characterized by continued substance use despite resulting in life disruption.

Drugs that reduce neural activity and slow body functions.

The diminishing effect with regular use of the same dose of a drug, requiring the user to take larger and larger doses before experiencing the drug’s effect.

An everyday term for compulsive substance use (and sometimes for dysfunctional behavior patterns, such as out-of-control gambling) that continue despite harmful consequences. (See also substance use disorder.)

The discomfort and distress that follow discontinuing an addictive drug or behavior.

Drugs that depress the central nervous system activity, reducing anxiety but impairing memory and judgment.

Opium and its derivatives; they depress neural activity, temporarily lessening pain and anxiety.

Drugs that excite neural activity and speed up bodily functions.

Psychedelic (“mind-manifesting”) drugs that distort perceptions and evoke sensory images in the absence of sensory input.

An altered state of consciousness reported after a close brush with death (such as cardiac arrest); often similar to drug-induced hallucinations.

The scientific study of the links between biological (genetic, neural, hormonal) and psychological processes. Some biological psychologists call themselves behavioral neuroscientists, neuropsychologists, behavior geneticists, physiological psychologists, or biopsychologists.

An integrated approach that incorporates biological, psychological, and social-cultural levels of analysis.

The differing complementary views, from biological to psychological to social-cultural, for analyzing any given phenomenon.

The brain’s ability to change, especially during childhood, by reorganizing after damage or by building new pathways based on experience.

Tissue destruction. Brain lesions may occur naturally (from disease or trauma), during surgery, or experimentally (using electrodes to destroy brain cells).

An amplified recording of the waves of electrical activity sweeping across the brain’s surface. These waves are measured by electrodes placed on the scalp.

A brain-imaging technique that measures magnetic fields from the brain’s natural electrical activity.

A series of X-ray photographs taken from different angles and combined by computer into a composite representation of a slice of the brain’s structure.

A technique for detecting brain activity that displays where a radioactive form of glucose goes while the brain performs a given task.

A technique that uses magnetic fields and radio waves to produce computer-generated images of soft tissue. MRI scans show brain anatomy.

A technique for revealing blood flow and, therefore, brain activity by comparing successive MRI scans. fMRI scans show brain function as well as structure.

Consists of the medulla, pons, and cerebellum; directs essential survival functions, such as breathing, sleeping, and wakefulness, as well as coordination and balance.

Found atop the brainstem; it connects the hindbrain with the forebrain, controls some motor movement, and transmits auditory and visual information.

Consists of the cerebral cortex, thalamus, and hypothalamus; manages complex cognitive activities, sensory and associative functions, and voluntary motor activities.

The central core of the brain, beginning where the spinal cord swells as it enters the skull; the brainstem is responsible for automatic survival functions.

The hindbrain structure that is the brainstem’s base; controls heartbeat and breathing.

The forebrain’s sensory control center, located on top of the brainstem; it directs messages to the sensory receiving areas in the cortex and transmits replies to the cerebellum and medulla.

A nerve network that travels through the brainstem into the thalamus; it filters information and plays an important role in controlling arousal.

The hindbrain’s “little brain” at the rear of the brainstem; its functions include processing sensory input, coordinating movement output and balance, and enabling nonverbal learning and memory.

Neural system located mostly in the forebrain — below the cerebral hemispheres — that includes the amygdala, hypothalamus, hippocampus, thalamus, and pituitary gland; associated with emotions and drives.

Two lima-bean–sized neural clusters in the limbic system; linked to emotion.

A limbic system neural structure lying below (hypo) the thalamus; it directs several maintenance activities (eating, drinking, body temperature), helps govern the endocrine system, and is linked to emotion and reward.

A neural center in the limbic system that helps process explicit (conscious) memories — of facts and events — for storage.

The intricate fabric of interconnected neural cells covering the forebrain’s cerebral hemispheres; the body’s ultimate control and information-processing center.

The portion of the cerebral cortex lying just behind the forehead. They enable linguistic processing, muscle movements, higher-order thinking, and executive functioning (such as making plans and judgments).

The portion of the cerebral cortex lying at the top of the head and toward the rear; it receives sensory input for touch and body position.

The portion of the cerebral cortex lying at the back of the head; it includes areas that receive information from the visual fields.

The portion of the cerebral cortex lying roughly above the ears; it includes the auditory areas, each of which receives information primarily from the opposite ear. They also enable language processing.

A cerebral cortex area at the rear of the frontal lobes that controls voluntary movements.

A cerebral cortex area at the front of the parietal lobes that registers and processes body touch and movement sensations.

areas of the cerebral cortex that are not involved in primary motor or sensory functions, but rather are involved in higher mental functions such as learning, remembering, thinking, and speaking.

The formation of new neurons.

The large band of neural fibers connecting the two brain hemispheres and carrying messages between them.

American Neurophysiologist

American Cognitive Neuroscientist who is an emeritus professor of psychology at the University of California

A condition resulting from surgery that separates the brain’s two hemispheres by cutting the fibers (mainly those of the corpus callosum) connecting them.

Our subjective awareness of ourselves and our environment.

The interdisciplinary study of the brain activity linked with cognition (thinking, knowing, remembering, and communicating).

The principle that information is often simultaneously processed on separate conscious and unconscious tracks.

A condition in which a person can respond to a visual stimulus without consciously experiencing it.

Processing multiple aspects of a stimulus or problem simultaneously.

Processing one aspect of a stimulus or problem at a time; generally used to process new information or to solve difficult problems.

A periodic, natural loss of consciousness — as distinct from unconsciousness resulting from a coma, general anesthesia, or hibernation. (Adapted from Dement, 1999.)

Our biological clock; regular bodily rhythms (for example, of temperature and wakefulness) that occur on a 24-hour cycle.

Rapid eye movement sleep; a recurring sleep stage during which vivid dreams commonly occur. Also known as paradoxical sleep, because the muscles are relaxed (except for minor twitches), but other body systems are active. (Sometimes called R sleep.)

The relatively slow brain waves of a relaxed, awake state.

Non-rapid eye movement sleep; encompasses all sleep stages except for REM sleep.

False sensory experiences, such as seeing something in the absence of an external visual stimulus.

Bizarre experiences, such as jerking or a feeling of falling or floating weightlessly, while transitioning to sleep. (Also called hypnic sensations.)

The large, slow brain waves associated with deep sleep.

A pair of cell clusters in the hypothalamus that controls circadian rhythm. In response to light, the SCN adjusts melatonin production, thus modifying our feelings of sleepiness.

Recurring problems in falling or staying asleep

A sleep disorder characterized by uncontrollable sleep attacks. The affected person may lapse directly into REM sleep, often at inopportune times.

A sleep disorder characterized by temporary cessations of breathing during sleep and repeated momentary awakenings.

A sleep disorder in which normal REM paralysis does not occur; instead, twitching, talking, or even kicking or punching may occur, often acting out one’s dream.

A sequence of images, emotions, and thoughts passing through a sleeping person’s mind.

The tendency for REM sleep to increase following REM sleep deprivation.

The process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment.

Sensory nerve endings that respond to stimuli.

The process by which our brain organizes and interprets sensory information, enabling us to recognize objects and events as meaningful.

Information processing that begins with the sensory receptors and works up to the brain’s integration of sensory information.

Information processing guided by higher-level mental processes, as when we construct perceptions drawing on our experience and expectations.

Conversion of one form of energy into another. In sensation, the transforming of physical energy, such as sights, sounds, and smells, into neural impulses the brain can interpret.

The study of relationships between the physical characteristics of stimuli, such as their intensity, and our psychological experience of them.

A German physicist, philosopher, and experimental psychologist.

The minimum stimulus energy needed to detect a particular stimulus 50 percent of the time.

A theory predicting how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise); assumes there is no single absolute threshold and that detection depends partly on a person’s experience, expectations, motivation, and alertness.

Below one’s absolute threshold for conscious awareness.

The activation, often unconsciously, of certain associations, thus predisposing one’s perception, memory, or response.

The minimum difference between two stimuli required for detection 50 percent of the time. We experience the difference threshold as a just noticeable difference (jnd).

German physician and experimental psychologist

The principle that, to be perceived as different, two stimuli must differ by a constant minimum percentage (rather than a constant amount).

Diminished sensitivity as a consequence of constant stimulation.

The distance from the peak of one light wave or sound wave to the peak of the next. Electromagnetic wavelengths vary from the short gamma waves to the long pulses of radio transmission.

The dimension of color that is determined by the wavelength of light; what we know as the color names blue, green, and so forth.

The amount of energy in a light wave or sound wave, which influences what we perceive as brightness or loudness. Intensity is determined by the wave’s amplitude (height).

The eye’s clear, protective outer layer, covering the pupil and iris.

The adjustable opening in the center of the eye through which light enters.

A ring of muscle tissue that forms the colored portion of the eye around the pupil and controls the size of the pupil opening.

The transparent structure behind the pupil that changes shape to help focus images on the retina.

The light-sensitive back inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual information.

The process by which the eye’s lens changes shape to focus images of near or far objects on the retina

Retinal receptors that detect black, white, and gray, and are sensitive to movement. Rods are necessary for peripheral and twilight vision, when cones don’t respond.

Retinal receptors that are concentrated near the center of the retina and that function in daylight or in well-lit conditions. Cones detect fine detail and give rise to color sensations.

The nerve that carries neural impulses from the eye to the brain.

The point at which the optic nerve leaves the eye, creating a “blind” spot because no receptor cells are located there.

The central focal point in the retina, around which the eye’s cones cluster.

The theory that the retina contains three different types of color receptors — one most sensitive to red, one to green, one to blue — which, when stimulated in combination, can produce the perception of any color.

The theory that opposing retinal processes (red-green, blue-yellow, white-black) enable color vision. For example, some cells are stimulated by green and inhibited by red; others are stimulated by red and inhibited by green.

an American-Canadian neurologist, was awarded the Nobel Peace Prize in physiology or medicine.

Swedish neurologist awarded the Nobel Peace Prize in physiology or medicine.

Nerve cells in the brain’s visual cortex that respond to specific features of the stimulus, such as shape, angle, or movement.

Processing multiple aspects of a stimulus or problem simultaneously.

The sense or act of hearing.

The number of complete wavelengths that pass a point in a given time (for example, per second).

A tone’s experienced highness or lowness; depends on frequency.

The chamber between the eardrum and the cochlea containing three tiny bones that concentrate the vibrations of the eardrum on the cochlea’s oval window.

The innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs.

A coiled, bony, fluid-filled tube in the inner ear; sound waves traveling through the cochlear fluid trigger nerve impulses.

The most common form of hearing loss, caused by damage to the cochlea’s receptor cells or to the auditory nerve; also called nerve deafness

A less common form of hearing loss, caused by damage to the mechanical system that conducts sound waves to the cochlea.

A device for converting sounds into electrical signals and stimulating the auditory nerve through electrodes threaded into the cochlea.

In hearing, the theory that links the pitch we hear with the place where the cochlea’s membrane is stimulated. (Also called place coding.)

In hearing, the theory that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch. (Also called temporal coding.)

The theory that the spinal cord contains a neurological “gate” that blocks pain signals or allows them to pass on to the brain. The “gate” is opened by the activity of pain signals traveling up small nerve fibers, and is closed by activity in larger fibers or by information coming from the brain.

Our sense of taste

Our sense of smell

Our movement sense; our system for sensing the position and movement of individual body parts.

Our balance sense; our sense of body movement and position that enables our sense of balance.

The principle that one sense can influence another, as when the smell of food influences its taste.

The influence of bodily sensations, gestures, and other states on cognitive preferences and judgments.