The Left and Right Brain Hemispheres: Independent Centers of Consciousness? :: Biology Health Term Papers

The Left and Right Brain Hemispheres: Independent Centers of Consciousness? "I'm of two minds on the matter." "I can't make up my mind." "I'm having an internal argument." Our language is full of idioms that make it sound as if there were two disagreeing voices inside our heads. Often, that is indeed how it feels. But is that sensation physiologically supported? Can a brain fight with itself? Can there be multiple independent centers of consciousness in a single head? Until the 1960s, there was no way for us to test this feeling of internal disagreement. But when a surgery aimed at alleviating epileptic seizures also isolated the two hemispheres of the patient's brain, science was surprisingly afforded that opportunity. Background The left and right hemispheres of the brain are connected by a dense bundle of neurons called the corpus callosum. This bundle is primarily responsible for communication of information between the two hemispheres, connecting them with approximately 200 million callosal axons (in humans.) (1) In some cases of multifocal epilepsy, the electrical discharges that cause seizures can start in one hemisphere and spread to the other by way of the corpus callosum, greatly increasing the severity of the fit. Sometimes this condition is unresponsive to medication, at which point the spasms can only be controlled with more drastic measures.(2) In 1961, Dr. Michael Gazzaniga performed an operation which had been pioneered on animals by Drs. Ronald Meyers and Roger Sperry, but which had never before been tested on human patients. In this procedure, called a commissurotomy, the surgeon opens the skull, lays back the brain coverings with a cerebral retractor, and cuts through the corpus callosum. While this prevents a seizure from spreading, it also prevents information from being passed between hemispheres. Thanks to Dr. P. J. Vogel, we now know that severing the anterior  ¾ of the corpus callosum can effectively stop the spread of a seizure, while allowing full communication between the hemispheres to remain. (3) However, the behavior of full-commissurotomy patients has been extensively documented, and provides fascinating insight into the specialization of the hemispheres, the nature of the brain, and the nature of consciousness itself. Results To understand these behaviors, one must first remember that neurological wiring of the body is, for the most part, contralateral. Signals travel from the left side of the body to the right hemisphere of the brain and back, and vice versa.