Lateralization

Lateralization, in neuroscience, is the tendency for certain cognitive functions or neural processes to be more specialized in one hemisphere of the brain than the other. This asymmetry is common across species and can pertain to language, emotion, perception, and motor control, among other functions.

In humans, language is the most well-known example of lateralization. The left hemisphere is typically dominant for language in the majority of individuals, involving areas such as Broca's and Wernicke's regions. Spatial attention, facial recognition, and some aspects of prosody and emotion processing often show a right-hemisphere bias, though there is considerable individual variability. Motor control is organized contralaterally, with each hemisphere primarily guiding movements on the opposite side of the body. Handedness is related to, but not determinative of, cerebral lateralization; most right-handers have left-hemisphere language dominance, while left-handers show a more variable pattern.

Researchers study lateralization using functional imaging (fMRI, PET), invasive methods like the Wada test, lesion studies, dichotic listening paradigms, and noninvasive brain stimulation. Lateralization can be absolute in a given function or show more diffuse, task-dependent patterns and may shift during development or in response to experience or injury.

Development and evolution contribute to lateralization. Genetic and environmental factors influence the emergence of hemispheric specialization, which is thought to improve processing efficiency and reduce redundancy. Cross-species observations reveal that lateralization supports specialized, parallel processing in complex behavior.

Altered or atypical lateralization has been reported in several neurodevelopmental and psychiatric conditions, though the causes and consequences remain areas of active research.