The Tell-Tale Brain

for pain “empathy” (in the anterior cingulate).

MOTOR NEURON A neuron that carries information from the central nervous system to a muscle. Also loosely used to include motor-command neurons, which program a sequence of muscle contractions for actions.

MU WAVES Some specific brain waves that are affected in autism. Mu waves may or may not be an index of mirror-neuron function, but they get suppressed both during action performance and action observation, suggesting a close link with the mirror-neuron system.

NATURAL SELECTION Sexual reproduction results in shuffling genes into novel combinations. Nonlethal mutations arise spontaneously. Those mutations or gene combinations that make some species better adapted to their current environment are the ones that survive more often because the parents survive and reproduce more often. The term is used in opposition to creationism (which holds that all species were created at once) and in contrast to artificial selection by humans to improve livestock and plants. Natural selection is not synonymous with evolution; it is a mechanism that drives evolutionary change.

NEURON Nerve cell. It is specialized for the reception and transmission of information, and is characterized by long fibrous projections called axons and shorter, branchlike projections called dendrites.

NEUROTRANSMITTER A chemical released by neurons at a synapse for the purpose of relaying information via receptors.

NEW PATHWAY Passes information from visual areas to the temporal lobes, via the fusiform gyrus, to help with the recognition of objects as well as with their meaning and emotional significance. The new pathway diverges into the “what” stream and the “how” stream.

OCCIPITAL LOBE One of the four subdivisions (the others being frontal, temporal, and parietal lobes) of each cerebral hemisphere. The occipital lobes play a role in vision.

OLD PATHWAY The older of two main pathways in the brain for visual processing. This pathway goes from the superior colliculus (a primitive brain structure in the brain stem) via the thalamus to the parietal lobes. The old pathway converges on the “how” stream to help move eyes and hands toward objects even when the person does not consciously recognize them. The old pathway is involved in mediating blindsight, when the new pathway alone is damaged.

PARASYMPATHETIC NERVOUS SYSTEM A branch of the autonomic nervous system concerned with the conservation of the body’s energy and resources during relaxed states. This system causes pupils to constrict, blood to be diverted to the gut for leisurely digestion, and heart rate and blood pressure to fall in order to diminish the load on the heart.

PARIETAL LOBE One of the four subdivisions (the others being frontal, temporal, and occipital lobes) of each cerebral hemisphere. A portion of the parietal lobe in the right hemisphere plays a role in sensory attention and body image, while the left parietal is involved in skilled movements and in aspects of language (object naming, reading, and writing). Ordinarily the parietal lobes have no role in the comprehension of language, which happens in the temporal lobes.

PERIPHERAL NERVOUS SYSTEM A division of the nervous system consisting of all nerves not part of the central nervous system (in other words, not part of the brain or spinal cord).

PHANTOM LIMB The perceived existence of a limb lost through accident or amputation.

PONS A part of the stalk on which the brain sits. Together with other brain structures, it controls respiration and regulates heart rhythms. The pons is a major route by which the cerebral hemispheres send information to and receive information from the spinal cord and the peripheral nervous system.

POPOUT TEST A test visual psychologists use to determine whether or not a particular visual feature is extracted early in visual processing. For example, a single vertical line will “pop out” in a matrix of horizontal lines. A single blue dot will “pop out” against a collection of green dots. There are cells tuned to orientation and color in low-level (early) visual processing. On the other hand, a female face will not pop out from a matrix of male faces, because cells responding to the sex of a face occur at a much higher level (later) in visual processing.

PREFRONTAL CORTEX See Frontal lobe.

PROCEDURAL MEMORY Memory for skills (such as learning to ride a bicycle), as opposed to declarative memory, which is storage of specific information that can be consciously retrieved (such as Paris being the capital of France).

PROTOLANGUAGE Presumed early stages of language evolution that may have been present in our ancestors. It can convey meaning by stringing together words in the right order (for example, “Tarzan kill ape”) but has no syntax. The word was introduced by Derek Bickerton of the University of Hawaii.

QUALIA Subjective sensations. (Singular: quale.)

RECEPTOR CELL Specialized sensory cells designed to pick up and transmit sensory information.

RECEPTOR MOLECULE A specific molecule on the surface or inside of a cell with a characteristic chemical and physical structure. Many neurotransmitters and hormones exert their effects by binding to receptors on cells. For example, insulin released by islet cells in the pancreas acts on receptors on target cells to facilitate glucose intake by the cells.

REDUCTIONISM One of the most successful methods used by scientists to understand the world. It only makes the innocuous claim that the whole can be explained in terms of lawful interactions between (not simply the sum of) the component parts. For example, heredity was “reduced” to the genetic code and complementarity of DNA strands. Reducing a complex phenomenon to its component parts does not negate the existence of the complex phenomenon. For ease of human comprehension, complex phenomena can also be described in terms of lawful interactions between causes and effects that are at the “same level” of description as the phenomenon (such as when your doctor tells you, “Your illness is caused by a reduction in vitality”), but this rarely gets us very far. Many psychologists and even some biologists resent reductionism, claiming, for example, that you cannot explain sperm if you know only its molecular constituents but not about sex. Conversely, many neuroscientists are mesmerized by reductionism for its own sake, quite independent of whether it helps explain higher-level phenomena.

REUPTAKE A process by which released neurotransmitters are absorbed at the