The Tell-Tale Brain: A Neuroscientist's Quest for What Makes Us Human

CROSS-MODAL Describes interactions across different sensory systems, such as touch, hearing, and vision. If I showed you an unnameable, irregularly shaped object, then blindfolded you and asked you to pick out the object with your hands from a collection of similar objects, you would use cross-modal interactions to do so. These interactions occur especially in the inferior parietal lobule (especially the angular gyrus) and in certain other structures such as the claustrum (a sheet of cells buried in the sides of the brain that receives inputs from many brain regions) and the insula.

DEFENSE MECHANISMS Term coined by Sigmund and Anna Freud. Information that is potentially threatening to the integrity of one’s “ego” is deflected unconsciously by various psychological mechanisms. Examples include repression of unpleasant memories, denial, rationalization, projection, and reaction formation.

DENDRITE A treelike extension of the neuron cell body. Along with the cell body, it receives information from other neurons.

ELECTROENCEPHALOGRAPHY (EEG) A measure of the brain’s electrical activity in response to sensory stimuli. This is obtained by placing electrodes on the surface of the scalp (or, more rarely, inside the head), repeatedly administering a stimulus, and then using a computer to average the results. The result is an electroencephalogram (also abbreviated EEG).

EPISODIC MEMORY Memory for specific events from your personal experience.

EXAPTATION A structure evolved through natural selection for a particular function that becomes subsequently used—and refined through further natural selection—for a completely novel unrelated function. For example, bones of the ear that evolved for amplifying sound were exapted from reptilian jaw bones used for chewing. Computer scientists and evolutionary psychologists find the idea irritating.

EXCITATION A change in the electrical state of a neuron that is associated with an enhanced probability of action potentials (a train of electrical spikes that occurs when a neuron sends information down an axon).

FRONTAL LOBE One of the four divisions of each cerebral hemisphere. (The other three divisions are the parietal, temporal, and occipital lobes.) The frontal lobes include the motor cortex, which sends commands to muscles on the opposite side of the body; the premotor cortex, which orchestrates these commands; and the prefrontal cortex, which is the seat of morality, judgment, ethics, ambition, personality, character, and other uniquely human attributes.

FUNCTIONAL MAGNETIC RESONANCE IMAGINING (FMRI) A technique—in which the baseline activity of the brain (with the person doing nothing) is subtracted from the activity during task performance—that determines which anatomical regions of the brain are active when a person engages in a specific motor, perceptual, or cognitive task. For example, subtracting a German brain’s activity from that of an Englishman might reveal the “humor center” of the brain.

FUSIFORM GYRUS A gyrus near the bottom inner part of the temporal lobe that has subdivisions specialized for recognizing color, faces, and other objects.

GALVANIC SKIN RESPONSE (GSR) When you see or hear something exciting or significant (such as a snake, a mate, prey, or a burglar), your hypothalamus is activated; this causes you to sweat, which changes your skin’s electrical resistance. Measuring this resistance provides an objective measure of emotional arousal. Also called skin conductance response (SCR).

HEMISPHERES See Cerebral hemispheres.

HIPPOCAMPUS A seahorse-shaped structure located within the temporal lobes. It functions in memory, especially the acquisition of new memories.

HOMININS Members of the Hominini tribe, a taxonomic group recently reclassified to include chimpanzees (Pan), human and extinct protohuman species (Homo), and some ancestral species with a mix of human and apelike features (such as Australopithecus). The hominins are thought to have diverged from the gorillas (Gorillini tribe).

HORMONES Chemical messengers secreted by endocrine glands to regulate the activity of target cells. They play a role in sexual development, calcium and bone metabolism, growth, and many other activities.