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The dual brain theory claims that the two cerebral hemispheres of the brain may sense and react to the environment independently from one another and that as a result of emotionally traumatic experience, one half may dominate the other in order to reduce the traumatized hemisphere's exposure. In essence, the person has two minds.

This theory is an extension of split-brain studies of epileptic patients having the corpus callosum severed in order to reduce seizures, but it has recently began to be studied in patients who have experienced traumatic events without any kind of brain surgery. In essence, this theory can apply to anyone.

Studies of healthy people with intact corpora callosa also indicate differing abilities or emotional responses associated with the two hemispheres. Studies using the Wada test and others are cited. In addition the theory draws upon research by Werner Wittling, Stuart Dimond, Roger Drake, Patrizio Tessoldi, Edward Fouty and Stephen E. Levick.

History
The first instances of this theory began during the nineteenth century. According to the theory, every person has two perfectly formed brains, each of which can be substituted for the other in case of some traumatic, unilateral brain injury. In this time, it was thought that each side of the brain was associated with a specific gender: the left corresponding with masculinity and the right with femininity and each half could function independently. The right side of the brain was seen as the inferior and thought to be prominent in women, savages, children, criminals, and the insane. A prime example of this can be seen in Robert Louis Stevenson’s Strange Case of Dr. Jekyll and Mr. Hyde.

Scientists of the time disagreed on whether these cases of hemisphere imbalance could be cured, but some did believe that there was an analogy between muscular exertion and brain activity, meaning a person could physically strengthen one side of their brain.

These studies continued up until about the 1920s before they died out because psychiatrists turned to psychological explanations and neurologists emphasized holistic brain dynamics. The brain duality was revived though in the 1960s with Roger Sperry’s split-brain experiments. In one of Sperry’s studies, he showed a split-brain patient a picture to his right brain and the left hemisphere, responsible for verbal responses, could not articulate what was being seen. But the patient’s left hand, connected to the right brain, was able to give a thumbs-up or thumbs-down showing whether he approved of the picture or not.

Epilepsy
The process that is mainly used to treat severe epileptic patients is corpus callosotomy. It usually involves the surgeon cutting the front two-thirds of the corpus callosum in hopes that it will greatly reduce the frequency of seizures. Later on, the remaining one-third can also be cut creating a complete severing of the two halves of the brain. This splitting of the two hemispheres of the brain usually leads to this dual brain theory, but of course, in can still occur in those with intact brains.

Dual Brain and Psychology
One of the biggest, if not the biggest, aspects of the Dual Brain theory is how it affects a person psychologically. The idea of having two independently thinking brains can affect how a person learns and how they function socially. Also, the way a person thinks changes drastically after a person experiences the dual brain effect.

Social Functionality
When a person experiences this dual brain phenomenon, either with an intact brain or from a split brain, there are some changes that occur in their everyday lives as they function in society. For example, Dr. Lu Moss Nelson recounts some odd behaviors that patients experienced after having their corpus callosum severed:


 * One patient reported that every time he wanted to smoke a cigarette, his right hand (his left brain) would reach for it, but his left hand (his right brain) would grab the cigarette and throw it away. He stated that he had no desire to quit smoking and he didn’t know why his left hand seemed to be acting all on its own. It would not let him smoke.
 * A female patient was getting dressed for a party. Every time her right hand (her left brain) would reach into her closet for her favorite dress, the one she wanted to wear, her left hand (right brain) would grab it and put it back. She didn’t understand why her left hand would not let her wear the dress she wanted to wear.
 * A patient reported that prior to his surgery he had no history of discord in his marital relationship, that in fact he and his wife rarely argued. But somehow, as he and his wife were discussing some difficult issues his left hand (right brain) attempted to strike his wife and his right hand (his left brain) grabbed it and prevented him from doing so. This patient reported that he had no conscious feelings of anger toward his wife and was frightened that his hand had tried to do such a terrible thing.
 * A post-operative patient reported that one morning she was awaked by her own hand. Her left hand (right brain) slapped her across the face. Her alarm clock had failed to go off; she had over slept for an appointment that she needed to keep. She could not understand why she had hit her own face. However, because she had awakened herself, she was able to get to her appointment on time.

Of Two Minds
Dr. Fredric Schiffer developed the dual brain model of psychology in his work with understanding how and when each half of the brain of a patient was dominating. One important aspect of this model is that often the two minds in a person quite different. In most cases he found that one mind tended to be more mature, reasonable, and living in the present. The other mind was often immature in its cognitive and emotional aspects. It was often this second mind that tended to be stuck back in the thought of whatever traumatic experience the patient had experienced.

To test this, Dr. Fredric Schiffer claims to have experimented with lateralizing glasses which restrict patients to one side of the visual field or the other, in turn stimulating the associated hemisphere. Schiffer claims this allowed some patients to experience the world through the more submissive or immature self and to compare differing experiences and changes in emotional moods, simply by switching between glasses. The glasses are fabricated simply by taping over the right or left halves of both lenses of typical safety glasses. The glasses function according the properties of the optic tract, whereby the right halves of both retinas (which see the left side of the field of view) are each connected to the right hemisphere, and the left halves (which see the right side of the field of view) are each connected to the left hemisphere, via optic nerves, which partially cross at the optic chiasm. Theoretically, the patient could then relativize experience and escape from a single viewpoint or life experience. In this manner a patient, through counseling, might begin a rapport between hemispheres in order to lead a more balanced and fruitful life.