Acetylcholine A neurotransmitter that plays an important role in attention, learning, and memory.

Amygdala Part of the limbic system always alert to threats.

Axon The long branch of a nerve cell that transmits information to other cells.

Conditioning A learned response to a stimulus that always precedes an event, as if the stimulus were the event itself.

Cortex The wrinkled layers of cells covering the surface of the brain, sometimes called gray matter.

Declarative Memory The conscious recollection of facts and events; also called explicit memory.

Dendrite A branch of a nerve cell that receives information from other cells.

Dopamine A “pleasure” neurotransmitter that plays a central role in the brain’s internal reward system.

Episodic Memory Conscious memory for what happened, where. Sometimes called “autobiographical memory.”

Frontal Lobes The most recently evolved section of the brain, used for conscious planning, problem solving, and control of emotion.

Glutamate A neurotransmitter that plays a central role in creating learning and memory pathways between brain cells.

Gray matter See cortex.

Habituation An unconscious form of learning by which our brain learns to ignore a repeatedly-applied stimulus once it has been categorized as non-threatening.

Hippocampus A part of the limbic system crucial for creating and accessing long-term memories.

Limbic System A collection of structures that play important roles in emotion, memory, and attention.

Long-term Potentiation The process underlying learning and memory by which one brain cell becomes sensitive to stimulation from a neighbor cell.

Myelin The insulation surrounding a brain cell’s axon.

Neurogenesis The production of new brain cells.

Neuron A nerve cell, or cell in the nervous system (which includes the brain). Often used interchangeably with brain cell.

Neurotransmitter A chemical messenger that brain cells use to communicate with one another.

Nondeclarative Memory Unconscious forms of memory and learning that influence behavior without our being aware of it. Also called implicit memory.

Priming A form of subliminal memory in which one piece of information can cue recall of another.

Procedural Memory Automatic memory for skills and habits, such as how to ride a bike or sign one’s name; also “muscle memory.”

Serotonin A “feel-good” neurotransmitter linked to mood, raised by antidepressants such as Prozac.

Subliminal Below the level of consciousness

Synapse The tiny gap between brain cells across which neurotransmitter chemicals convey messages.

White Matter The part of the brain beneath the cortex that consists mostly of brain cell axons sheathed in myelin.

Working Memory A short-term memory system for holding information “online” and manipulating it to solve problems.