The learned abilities to move some part of the body, in actions ranging from a large leap to a flicker of the eyelid. (The word motor here refers to movement of muscles.)

A process that stimulates the body’s immune system by causing production of antibodies to defend against attack by a particular contagious disease. Creation of antibodies may be accomplished either naturally (by having the disease), by injection, by drops that are swallowed, or by a nasal spray. (These imposed methods are also called vaccination.)

The ability to focus the two eyes in a coordinated manner in order to see one image.

Physical abilities involving large body movements, such as walking and jumping. (The word gross here means “big.”)

When applied to brain development, the process by which unused connections in the brain atrophy and die.

The intersection between the axon of one neuron and the dendrites of other neurons.

A life-threatening injury that occurs when an infant is forcefully shaken back and forth, a motion that ruptures blood vessels in the brain and breaks neural connections.

A situation in which a seemingly healthy infant, usually between 2 and 6 months old, suddenly stops breathing and dies unexpectedly while asleep.

A disease of severe protein-calorie malnutrition during early infancy, in which growth stops, body tissues waste away, and the infant eventually dies.

A condition in which a person does not consume sufficient food of any kind. This deprivation can result in several illnesses, severe weight loss, and even death.

The area of the cortex at the very front of the brain that specializes in anticipation, planning, and impulse control.

The pathway across which neurotransmitters carry information from the axon of the sending neuron to the dendrites of the receiving neuron.

A serious medical condition in early infancy, when the baby does not gain weight as rapidly as he or she is expected to.

A stage of sleep characterized by flickering eyes behind closed lids, dreaming, and rapid brain waves.

The failure of children to grow to a normal height for their age due to severe and chronic malnutrition.

The tendency for children to be severely underweight for their age as a result of malnutrition.

When two or more people sleep in the same bed. If one of those people is an infant, some researchers worry that the adult will roll over on the infant.

A brain chemical that carries information from the axon of a sending neuron to the dendrites of a receiving neuron.

The great but temporary increase in the number of dendrites that develop in an infant’s brain during the first two years of life.

The mental processing of sensory information when the brain interprets a sensation.

One of billions of nerve cells in the central nervous system, especially in the brain.

The outer layers of the brain in humans and other mammals. Most thinking, feeling, and sensing involves the cortex.

Brain functions that depend on particular, variable experiences and that therefore may or may not develop in a particular infant.

The response of a sensory system (eyes, ears, skin, tongue, nose) when it detects a stimulus.

A disease of chronic malnutrition during childhood, in which a protein deficiency makes the child more vulnerable to other diseases, such as measles, diarrhea, and influenza.

Brain functions that require certain basic common experiences (which an infant can be expected to have) in order to develop normally.

A fiber that extends from a neuron and transmits electrochemical impulses from that neuron to the dendrites of other neurons.

A biological mechanism that protects the brain when malnutrition disrupts body growth. The brain is the last part of the body to be damaged by malnutrition.

Physical abilities involving small body movements, especially of the hands and fingers, such as drawing and picking up a coin. (The word fine here means “small.”)

A custom in which parents and their children (usually infants) sleep together in the same room.

The inborn drive to remedy a developmental deficit; literally, to return to sitting or standing upright after being tipped over. People of all ages have self-righting impulses, seeking emotional as well as physical balance.

A fiber that extends from a neuron and receives electrochemical impulses transmitted from other neurons via their axons.

A point on a ranking scale of 0 to 100. The 50th percentile is the midpoint; half the people in the population being studied rank higher and half rank lower.