APA Dictionary of Psychology

systematic differences in structure, function, or neurochemical architecture between the left and right hemispheres of the brain. These asymmetries are a fundamental organizational principle of the nervous system and reflect lateralization, in which certain cognitive, sensory, motor, or emotional processes are preferentially supported by one hemisphere rather than the other. Brain asymmetry is studied at multiple levels, including anatomical (e.g., regional volume, cortical thickness), functional (e.g., hemispheric dominance for language or attention), and developmental differences. While some asymmetries are consistent across individuals, others vary by task, development, handedness, sex, or clinical condition. Also called cerebral asymmetry or hemispheric asymmetry. See also dominance; hemispheric lateralization.