Left Brain Vs. Right Brain

The human brain is divided into left and right cerebral hemispheres that are have both differences as well as similarities in their roles and functions (Pinel, 2006). The two hemispheres are connected by cerebral commissures which allow for both hemispheres to communicate. The commissures consist of nerve fibers with millions of axons that pass information from one hemisphere to the next (Andrewes, 2002). Although the left hemisphere is often referred to as the dominant hemisphere, both the left and the right sides of the brain participate in the general functions of movement, memory, vision, and audition (Stirling, 2002). The left hemisphere has dominance in the areas of recognizing words and letters, comprehending language sounds, complex movements, having verbal memory, and the functions of speech, reading, writing, and arithmetic (Pinel, 2006). The right hemisphere has dominance in the areas of geometric patterns and emotional expressiveness, music enjoyment (not interpretation as this occurs in the left hemisphere), nonverbal memory, geometry, direction, distance, movement in special patterns, and emotional content (Pinel, 2006).

Normal individuals will demonstrate some asymmetry in the lateralization of the brain and this can be observed using dichotic listening tasks in which sounds are played in one ear and then played in the other ear to measure how they are processed (Stirling, 2002). Typically the right ear will demonstrate a small level of dominance as the left brain directly receives the input (right ear managed by left hemisphere, left ear managed by right ear, left hemisphere in charge of language functions) and it is hypothesized that this results in an decreased time for word recognition (Stirling, 2002). This is very interesting as I have a real life example of how this has affected my son. My seven year old was diagnosed as being on the autistic spectrum when he was four and shortly after his fifth birthday I placed him in a sensory learning institute for a month long session to “rewire” how his brain hemispheres communicate with each other. My son had a language delay and the professionals at the Sensory Learning Institute (2008) recommend a procedure in which auditory training is achieved by first documenting a “perception map” to find the dominant ear (which is typically the left ear for these children) and then retraining the other ear (typically the right ear) to manage sounds. The theory is that the children can improve their language capabilities by having a dominant right ear so that the sounds are delivered directly to the left brain for rapid processing. My personal experience with this program, although it was quite costly and not covered by insurance, was that it was a success.

Although the left brain is considered to be dominant, both hemispheres of the brain working together are preferable. This is not always possible due to circumstances such as brain injury, strokes, and surgeries to remove tumors or halt seizures (Stirling, 2002). Andrewes (2002) noted that the Wada technique can be used to study lateralization by anesthetizing on side of the brain to demonstrate the loss of functionality in one brain hemisphere. The Wada technique has been used to deactivate the language cortex to determine the hemisphere with language dominance before any epilepsy surgeries are performed (Abou-Khalil, 2007). This procedure is invasive and consists of an anesthetic agent being injected into the internal carotid artery so that a cerebral angiogram can be conducted. There are many variations in this procedure regarding which side receives injection first, the dosage, the type of anesthesia, and the type of tests that are administered after the injection. Additionally, noninvasive procedures that can detect the language cortex activation, such as functional MRIs or transcranial Dopplers, are becoming more popular and soon may replace the use of the Wada test.

Abou-Khalil, B. (2007). An update on determination of language dominance in screening for epilepsy surgery: The wada test and newer noninvasive alternatives. Epilepsia (Series 4), 48(3), 442-455.

Andrewes, D. (2002) Neuropsychology: From theory to practice. New York: Psychology Press.

Pinel, John P. J. (2006). Biopsychology with “beyond the brain and behavior” (6th ed.). Boston: Allyn and Bacon.

Sensory Learning Center. (2008, March 25). Frequently asked questions. Retrieved from: http://www.sensorylearning.com.

Stirling , J. (2002). Introducing neuropsychology. New York: Psychology Press.

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