ミラーニューロンと解離 25

 Split brain - A putative biological model for the multiplicity of personality

I propose that so-called “split-brain experiment” (Gazzaniga, 1970) , indicates something akin to the multiplicity of the personalities in different locations in the brain, and I consider that state as a step toward the biological model of DID.

Gazzaniga, M. S. (1970). The Bisected Brain. Appleton Century-Crofts.

There seems to be an increase of attention to the issue of split brain (Haan, et al. 2020). It is because the surgical disconnection of the cerebral hemispheres creates a splendid opportunity to study the neurological mechanisms of consciousness in its potential dual states (Gazzaniga, 2000).
Gazzaniga, MS (1995) Principles of Human Brain Organization Derived from Split-Brain Studies. Review Neuron, Vol. 14, 217-228.

After the two hemispheres are disconnected, the person verbal IQ of a patient remains intact (Nass and Gazzaniga, 1987) and problem-solving capacity remains unchanged for the left speaking hemisphere (Ledoux, et al.,1988). However, with a proper set of examination, each hemisphere has a separate mind. “Cortical disconnection produces two independent sensory information processing systems … (Gazzaniga, 1995)”, with each hemisphere having its own set of specialized capacities, e.g., language and speech, problem solving capacities for the left, and facial recognition, attentional monitoring, etc for the right. When tested separately, right hemisphere is seriously impoverished in cognitive tasks. It is poor at problem solving and may other mental activities (Gazzaniga.2000). Therefore, it has been debatable whether the right, mute hemisphere has its conscious equal to its counterpart.
Gazzaniga M (2000) Cerebral specialization and interhemispheric communication - Does the corpus callosum enable to human condition? Brain. 123:1293-1326. 
Nass, R, Gazzaniga, M (2011) Cerebral Lateralization and Specialization in Human Central Nervous System. Handbook of Physiology. 
Ledoux, JE, Risse GL, et al. (1977) Cognition and commissurotomy. Brain. 100.87-104.

Joseph LeDoux tackled this issue and stated that brain bisection produces a state of double consciousness (Ledoux, et al.1977). In their experiment with a patient “P.S.” with a split brain, they concluded that the right hemisphere in that patient has a sense of self with its own feeling.

Personally, the author considers that it is still debatable if this state of right brain is emancipated enough to be called a conscious mind. It sounds much more like a part of personality, needing the counterpart (left brain) to be supplemented to function as a while, just as van der Hart defined as a “part of personality”.

Haan, EHF, Corballis, PM. et al (2020) Split-Brain: What We Know Now and Why This is Important for Understanding Consciousness Neuropsychology Review (2020) 30:224–233.
LeDoux, JE, Wilson,DH, Gazzaniga, MS (1977) A Divided Mind: Observations on the Conscious Properties of the Separated Hemispheres. Ann Neurol. 2:417-421. 

To summarize, the split-brain states seems to create two independent minds. The speaking left hemisphere appears normal with intact intelligence, which is largely unaware of its counterpart, right brain, except for the “emotional significance” of its experience (LeDeux, 1996).

Ledoux, J.(1996) The Emotional Brain. The Mysterious Underpinnings of Emotional Life. The Touchstone.

   Although it is still debatable whether the right brain can claim that it is emancipated enough to be called a “personality”, at least two issues are obvious.
   When dissected, the neural network consisting of two connected hemispheres would become two independent minds. It appears to be crucial for a mind to be conscious to have a set of one hemisphere, one thalamus, and a limbic system including amygdala and hippocampus which are connected to each other. As Tononi’s information system asserts, it is not the localization but the connection of system that creates the mind. In order to consider the neural correlate of a personality, this “set” is a crucial component.