Cerebral dominance

Definition

Cerebral dominance refers to the dominance of one cerebral hemisphere over the other in the control of cerebral functions.

Description

Cerebral dominance is the ability of one cerebral hemisphere (commonly referred to as the left or right side of the brain) to predominately control specific tasks. Accordingly, damage to a specific hemisphere can result in an impairment of certain identifiable functions. For example, trauma to the left hemisphere can impair functions associated with speech, reading, and writing. Trauma to the right hemisphere can result in a decreased ability to perform such tasks as judging distance, determining direction, and recognizing tones and similar artistic functions.

Cerebral dominance and handedness

Cerebral dominance is also related to handedness—whether a person has a strong preference for the use of their right or left hand. More than 90% of people are right-handed and in the vast majority of these individuals, the left hemisphere controls language-related functions.

In left-handed individuals, however, only about 75% have language functions predominantly controlled by the left hemisphere. The remainder of left-handed individuals have language functions controlled by the right hemisphere, or do not have a dominant hemisphere with regard to language and speech.

A very small percentage of people are ambidextrous, having no preference for performing tasks with either hand.

One aspect of cerebral dominance theory that has received considerable research attention is the relationship between a lack of cerebral dominance and dyslexia . Some research data suggest that indeterminate dominance with regard to language—a failure of one hemisphere to clearly dominate language functions—results in dyslexia. Evidence to support this hypothesis is, however, not uniform or undisputed.

In general terms, for right-handed people the left side of the brain is usually associated with analytical processes while the right side of the brain is associated with intuitive or artistic abilities. The data to support such generalizations is, however, not uniform.

The cortex is divided into several cortical areas, each responsible for separate functions such as planning of complex movements, memory, personality, elaboration of thoughts, word formation, language understanding, motor coordination, visual processing of words, spatial orientation, and body spatial coordination. The association areas of the cortex receive and simultaneously analyze multiple sensations received from several regions of the brain. The brain is divided into two large lobes interconnected by a bundle of nerves, the corpus callosum. It is now known that in approximately 95% of all people, the area of the cortex in the left hemisphere can be up to 50% larger than in the right hemisphere, even at birth. Both Wernicke's and the Broca's areas (specific anatomical regions) are usually much more developed in the left hemisphere, which gave origin to the theory of left hemisphere dominance. The motor area for hand coordination is also dominant in nine of out 10 persons, accounting for the predominance of right-handedness among the population.

Studies also show that the non-dominant hemisphere plays an important role in musical understanding, composition and learning, perception of spatial relations, perception of visual and other esthetical patterns, understanding of connotations in verbal speeches, perception of voice intonation, identification of other's emotions and mood, and body language.

One hindrance to the acceptance of data relating to cerebral dominance is the fact that social pressure to conform to the norm can drive some left-handed people to adopt the predominant use of their right hand.