Twins that emerge from one zygote that splits for unknown reasons. Also called Monozygotic twins.

The sum of an individual's own reproductive success plus the effects the organism has on the reproductive success of related others.

Destroying a piece of the brain.

A densely connected network of structures roughly located along the border between the cerebral cortex and deeper subcortical areas.

The segment of the brain stem that lies between the hindbrain and the forebrain.

Neurons that are activated by performing an action or by seeing another monkey or person perform the same action.

Principle stating that heritable characteristics that provide a survival reproductive advantage are more likely than alternative characteristics to be passed on to subsequent generations and thus come to be selected over time.

Bundles of neuron fibers (axons) that are routed together in the peripheral nervous system.

The formation of new neurons in the brain.

Individual cells in the nervous system that receive, integrate, and transmit information.

Chemicals that transmit information from one neuron to another.

The branch of the autonomic nervous system that generally conserves bodily resources.

Left-right imbalances between the cerebral hemispheres in the speed of visual or auditory processing.

All those nerves that lie outside the brain and spinal cord.

The ways in which a person's genotype is manifested in observable characteristics.

The master gland of the endocrine system; it releases a great variety of hormones that fan out through the body, stimulating actions in the other endocrine glands.

Characteristics that are influenced by more than one pair of genes.

A voltage change at the receptor site on a postsynaptic cell membrane.

A gene whose influence is masked when paired genes are different (heterozygous).

The stable, negative charge of a neuron when it is inactive.

A process in which neurotransmitters are sponged up from the synaptic cleft by the presynaptic membrane.

The cell body of a neuron; it contains the nucleus and much of the chemical machinery common to most cells.

The system of nerves that connect to voluntary skeletal muscles and to sensory receptors.

A procedure in which the bundle of fibers that connects the cerebral hemispheres (the corpus callosum) is cut to reduce the severity of epileptic seizures.

The branch of the autonomic nervous system that mobilizes the body's resources for emergencies.

A junction where information is transmitted from one neuron to the next.

A microscopic gap between the terminal button of a neuron and the cell membrane of another neuron.

Small knobs at the end of axons that secrete chemicals called neurotransmitters.

A male sex hormone produced by the testes; women secrete smaller amounts of testosterone from the adrenal cortex and ovary.

A new technique that permits scientists to temporarily enhance or depress activity in a specific area of the brain (TMS).

A research design in which hereditary influence is assessed by comparing the resemblance of identical twins and fraternal twins with respect to a trait.

A one-celled organism formed by the union of a sperm and an egg.