cerebellum Also known as the "little brain," the cerebellum is divided by the primary fissure into anterior and posterior lobes. Other fissures further segment these lobes into several smaller lobules. A thin longitudinal strip traverses the midline and is known as the vermis. The cerebellar cortex contains several different neuron types, including Purkinje neurons, the sole output source. Functionally, the cerebellum has been traditionally viewed as involved only in motor control; however, a new understanding has come to include multiple cognitive functions, such as language and attention.

chromosomes Long thread-like associations of genes found in the nucleus of all eukaryotic cells. Chromosomes consist of DNA and protein.

event-related potential technique A neuroimaging method that records electrical activity from the scalp via electrodes as an individual performs a task. Signal amplitudes and latencies are believed to represent net electrical fields associated with the activity of a population of neurons.

functional magnetic resonance imaging A neuroimaging technique that uses the differing magnetic susceptibility of oxyhemoglo-bin and deoxyhemoglobin in the blood to detect when and where oxygen is used in the brain, typically as an individual performs a cognitive task.

gene A sequence of DNA that indirectly produces a protein and is located on chromosomes.

genetic linkage analysis with disorder loci The preferential association of a particular gene, or set of genes, with a particular disorder than would be expected by chance alone.

gliosis The presence of glial cells in unexpected locations in neuronal tissue usually as the result of injury or insult.

limbic system A constellation of cortical and subcortical brain structures thought to be instrumental in memory and emotion. Traditionally, the limbic lobe includes the parahippocam-pal gyrus, the cingulate gyrus, and the subcallosal gyrus; subcortical structures include the hippocampus, amygdala, and parts of the hypothalamus.

magnetic resonance imaging A noninvasive technique used to produce high-resolution images of body tissues, especially soft tissues such as the brain. A large magnet is used to polarize hydrogen atoms in the tissues and radio frequencies are used to measure the nuclear magnetic resonance of the protons within the tissue.

pleiotropy The condition in which a single gene or gene pair exerts effects on multiple functions and/or in multiple cell types often at different times.

repetitive behaviors and stereotyped patterns Interests, motor movements (e.g., arm flapping and rocking), and rituals that are performed repetitively and inflexibly and do not serve any apparent function.

Autism is a biological disorder with a clinical onset in the first years oflife that persists, to varying degrees, throughout life. It is characterized by abnormality in reciprocal social interaction, communication, and language development as well as by repetitive and stereotyped behavior. These abnormalities are caused by defects in multiple areas of the brain. The prevalence is 1:600, making it one of the most common neurobiological disorders of infancy and early childhood. It is one of five pervasive developmental disorders (PDDs), along with Rett's syndrome, Asperger's syndrome, child

Encyclopedia of the Human Brain Volume 1

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hood disintegrative disorder, and pervasive developmental disorder not otherwise specified (PDD-NOS), listed in the Diagnostic and Statistical Manual IV. Taken together, the prevalence of a PDD is 1:160. The degree to which autism, Asperger's, and PDD-NOS disorders with behavioral profiles that overlap, may be variants on a single biological theme, or constitute unique etiologies, is still under debate.



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