The Dragons of Eden

by Carl Sagan

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  Glossary

  Accessing Computer jargon for making contact with information stored elsewhere.

  AFFECT (noun) A feeling of emotion, particularly a strong one.

  ALEXIA A weakening or loss of the ability to comprehend written or printed words and sentences. Compare with aphasia.

  AMESLAN American sign language, widely used by persons with impaired speech and hearing.

  AMYGDALA An almond-shaped component of the limbic system adjoining the temporal lobe of the neocortex.

  ANAGLYPH A two-dimensional stereo representation of a three-dimensional image; most often composed of red and green dots, and viewed with red and green eye-glasses.

  ANTERIOR COMMISSURE A relatively minor bundle of nerve fibers that connects the left and right cerebral hemispheres of the neocortex. Compare with corpus callosum.

  APHASIA Generally, a weakening or loss of the ability to articulate ideas by language in any form. It is sometimes used more narrowly to indicate the inability to recognize spoken words. Compare with alexia.

  BILATERAL On both sides.

  BITS Units of binary information. One bit is the answer to a single yes or no question.

  BRAINSTEM See Hindbrain.

  BROCA’S AREA A portion of the neocortex intimately connected with speech.

  BUFFER DUMPING The accessing (q.v.) or disposal of information temporarily deposited in a short-term memory.

  CC Abbreviation for cubic centimeter.

  CEREBELLUM A brain mass lying in the back of the head underneath the posterior cerebral cortex and above the pons and medulla in the hindbrain. Like the neocortex, it has two hemispheres.

  CEREBRAL CORTEX In humans and higher mammals the large outer layer of the cerebral hemispheres, in major part responsible for our characteristically human behavior. Sometimes synonymous with neopallium or neocortex (q.v.).

  CETACEA An order of aquatic mammals that includes whales and dolphins.

  CHROMOSOMES The long strands of hereditary material containing the genes, and composed exclusively of nucleic acids.

  CONVOLUTION See Gyrus.

  CORPUS CALLOSUM The great commissure, or bundle of nerve fibers, which is the principal cabling between the left and right hemispheres of the cerebral cortex.

  CRANIOTOMY The cutting or removal of part of the skull, generally as an antecedent to brain surgery.

  DNA Deoxyribonucleic acid. See Nucleic acids.

  ELECTRODE A solid electrical conductor through which an electric current moves. Electrical currents in the brain are sensed by an electroencephalograph through its electrodes.

  ELECTROENCEPHALOGRAPH (EEG) A device consisting of amplifiers and a pen automatically writing on a rotating drum, used for recording the electrical currents in the brain conducted to the device by electrodes attached to the surface of the head. It is useful for medical diagnosis and for studies of the function of the brain.

  ENDOCAST A mold of an interior; in this book, a mold of the interior of a fossil braincase.

  ENDOCRANIAL Within the skull.

  ENDORPHINS Small internally produced brain proteins which can induce a variety of emotional or other states in animals.

  EQUIPOTENT Having equal ability; in particular, the view that for certain cognitive or other functions any part of the brain can substitute for any other.

  EXTIRPATION The entire removal of a unit of the brain, usually by surgical procedures.

  EXTRAGENETIC INFORMATION Information carried outside the genes—generally in brains and cultures.

  EXTRASOMATIC INFORMATION Information carried outside the body (for example, the contents of books).

  FOREBRAIN The evolutionarily most recent of the three major divisions of the vertebrate brain. Also called the prosencephalon. It is divided in turn into the R-complex, limbic system, and neocortex.

  FRONTAL LOBE Approximately, the portion of the neocortex beneath the forehead.

  GAMETES Mature sperm or egg cells capable of participating in fertilization. They contain a haploid (q.v.) number of chromosomes.

  GYRUS One of the prominent rounded elevations on the surface of the neocortex. Also called convolution.

  HAPLOID Having a number of chromosomes equal to half the number in an ordinary body or somatic cell. For example, in human beings each somatic cell has 46 chromosomes but each gamete (q.v.) has 23 chromosomes.

  HINDBRAIN The most ancient part of the brain, including the pons, cerebellum, medulla oblongata, and the upper portion of the spinal cord. It is also called the brainstem or the rhombencephalon.

  HIPPOCAMPAL COMMISSURE A relatively minor bundle of nerve fibers which connects the left and right hemispheres of the cerebral cortex near the hippocampus. Compare with corpus callosum.

  HIPPOCAMPUS A structure in the limbic system connected with memory.

  HYPOTHALAMUS A portion of the limbic system lying below
the thalamus which, among other functions, helps to regulate bodily temperature and metabolic processes.

  KG Abbreviation for kilogram.

  LATERALIZATION The separation of function between two sides, especially the left and right hemispheres of the neocortex.

  LESION A cut, wound, or injury. Some brain lesions occur by accident and some by surgical procedure.

  LIMBIC SYSTEMS The part of the forebrain intermediate in locale and antiquity between the R-complex and the neocortex.

  LOBES OF THE NEOCORTEX See Frontal lobe, Occipital lobe, Parietal lobe, and Temporal lobe.

  LOBOTOMY A surgical incision into or lesion of one of the neocortical lobes (q.v.).

  LOCALIZATION OF BRAIN FUNCTION The finding that certain parts of the brain perform certain specific functions. It is the opposite of the equipotent (q.v.) hypothesis.

  LONG-TERM MEMORY Memory retained for substantial periods of time—for example, more than a day.

  M Abbreviation for meter.

  MEDULLA OBLONGATA (sometimes called simply MEDULLA) The portion of the brain at the region of its connection with the spinal cord. It is a part of the hindbrain.

  MICROCEPHALIC One with an abnormally small head. The condition is often associated with significant mental impairment.

  MIDBRAIN The middle region of the vertebrate brain, between the hindbrain and forebrain. Also called the mesencephalon.

  MOTOR CORTEX The portion of the neocortex concerned with motion and coordination of the limbs.

  MUTATIONS Inheritable changes in the nucleic acids of chromosomes.

  NATURAL SELECTION The principal method of biological evolution, as first described by Darwin and Wallace. The preferential survival and reproduction of organisms fortuitously better adapted to their environments than their competitors.

  NEOCORTEX The outermost, evolutionarily most recent part of the cerebral cortex. Sometimes used as synonymous with cerebral cortex.

  NEURAL CHASSIS The combination of spinal cord, hind-brain, and midbrain.

  NEURON or NEURONE A nerve cell, the basic unit of the nervous system, and the fundamental building block of the brain.

  NICHE, ECOLOGICAL An organism’s role in nature.