Split-Brain Functioning

As stated earlier, an individual's handedness seems related to how certain functions are distributed between the left and right hemispheres, and while there are numerous exceptions to every general rule about the asymmetry of certain functions, there are some very commonly lateralized functions. The most obvious of these is language.

In those who are right-handed, with very few exceptions, speech functions are primarily located in the left hemisphere. This is also the case for most left-handers, but many more left-handers than right-handers seem to have speech functions located either mostly in the right hemisphere or distributed more evenly between the hemispheres. In general, it seems that left-handers are more likely to have an even distribution of certain behavior functions between the left and right hemispheres than are right-handers.

Injury of the left hemisphere, or presentation of information to the right hemisphere alone, often results in impaired speech, reading abilities, naming of objects, or comprehending spoken language. The left hemisphere in most human beings seems to exert primary control over linguistic abilities, as well as numerical and analytic behaviors. The right hemisphere in most human beings seems to exert primary control over nonverbal activities such as the ability to draw and copy geometric figures, various musical abilities, visual-spatial reasoning and memory, and the recognition of form using vision and touch.

There is also evidence that the two hemispheres of the brain process information differently. It seems that the right hemisphere tends to process information in a more simultaneous manner, synthesizing and bringing diverse pieces of information together. The left hemisphere seems to process information in a logical and sequential manner, proceeding in a more step-by-step manner than the right hemisphere.

In terms of the processing, experiencing, and expression of emotion, there are some very intriguing findings. Based on a number of studies looking at the location of lesions in individuals who showed uncontrollable laughter or crying, it seems the left hemisphere is highly involved in the expression of positive emotions, while the right hemisphere is highly involved in the expression of negative emotions. Some researchers believe that the two hemispheres of the brain usually serve to mutually inhibit each other so that there is a balance, and uncontrollable emotional outbursts are rare. Based on tests with normal subjects, it seems that the right hemisphere plays a major role in the perception of emotion. In sum, much evidence indicates that the right hemisphere is more involved than the left in processing emotional information and in producing emotional expressions, but the left hemisphere seems to play a unique role in expressing positive emotions. The reader should note that research on brain asymmetry and emotion is relatively new and findings should be interpreted with caution.