Split Brain Consciousness Trevor Norlock Daniel Bowling Adrienne Keener Dina Saab

Introduction In a Healthy brain, stimuli is communicated between the two hemispheres via the corpus callosum When this is severed, a split brain exists Epilepsy- Seizures trigger massive neuron activation in one hemi, that travels to the other hemi via the corpus callosum

Introduction To prevent these seizures, neurosurgeons can perform a commissurotomy The surgeon opens the skull, lays back the brain's coverings and, with a tool called a cerebral retractor, exposes the corpus callosum between the two hemispheres The doctor snips through the corpus callosum, severing communication between the hemispheres and preventing the transfer of seizures

History The "split brain" was first discovered in the laboratory by Roger Sperry and Ronald Meyers Initially they began experimenting with cats, and later proceeded to study monkeys In 1961 the first human patient was subject to the split brain surgery.

History The procedure worked well as a "cure" for patients who suffered from severe epilepsy Patients were not able to communicate information from one hemisphere to the other, almost as though they now had two separate brains.

History How (and what) the hemispheres communicate would provide valuable insight into the "mind" of a split brain patient How did a commissurotomy affect one's perceptions of the outside world? Interestingly enough, the centers for speech interpretation and production are located in the left hemisphere

History Similarly, if the patient is blindfolded and a familiar object, such as a toothbrush, is placed in his left hand, he appears to know what it is; for example by making the gesture of brushing his teeth. But he cannot name the object to the experimenter If asked what he is doing with the object, gesturing a brushing motion, he has no idea But if the left hand gives the toothbrush to the right hand, the patient will immediately say "tooth brush"

History Micheal Gazzaniga, who did his graduate work in Sperry's laboratory, did further experiments which showed the attempts of the left hemisphere to compensate for it's lack of information, as well as attempts by the right hemisphere to get it's knowledge conveyed The idea of an ‘interpreter” These experiments provided insight into the functioning's of the two hemispheres and how they are different

Implications for Theories of Consciousness Split brain research has sparked questions regarding human conscious experience Is consciousness a function of one or both hemispheres? What role does each hemisphere play in conscious experience? Do split brain patients exhibit different behavioral patterns compared to normals? Is the consciousness of split brain patients different than normals?

Mental Duality Hypothesis Each hemisphere has a separate consciousness. The function of the corpus callosum is duplicative rather than integrative. (Puccetti) In the intact brain the conscious experiences of the two hemispheres are kept in synchrony by the corpus callosum, so the duality is not detected

Split Brain and Consciousness Experiments conducted on split brain subjects have shown that each hemisphere can independently perceive stimuli and execute motor actions Ex: Gazzaniga’s chicken claw snowy scene experiment Ex: Right hand picks up paper to read and left hand takes it and throws it on the ground This does not necessarily imply that the two hemispheres have independent consciousness

Global Hypothesis Consciousness in the intact brain is an emergent result of the interaction between the two hemispheres The corpus callosum serves to integrate the lateralized functions of the two hemispheres In the split brain, unified conscious experience is maintained by interhemispheric subcortical connections and various bilateral representations (Sperry)

The Intact Brain and Consciousness The Left and Right hemispheres have different strategies for dealing with information Our conscious experience is an integration of the functions of both hemispheres

Associative Processing Semantic Networks Spreading Activation theory Evidence: Semantic Priming Effect – Faster responses when 2 words are semantically related then when they are not

Interpretation Strategies Lateralized semantic priming tasks have revealed that: LH: Narrow spread of semantic activation Better for making close associations Protects the spread from going too far and allows integration of new info with old RH: Diffuse spread of semantic activation Better for making remote associations Promotes creative, new and uncommon associations

Evidence for Different strategies Electrophysiological studies provide evidence that: Close prototypical associations are preferentially processed by the Left Hemisphere Remote, less prototypical associations are preferentially processed by the Right Hemisphere

Finding Patterns When perceiving patterns in data we are prone to making the following types of errors: TYPE I: Perceiving a pattern where none exists “False Alarm” TYPE II: Not perceiving a pattern where one exists “Miss”

Interpreters LH: Involved in preserving the current paradigm and suppressing opposing evidence RH: Detecting anomalies and trying to force a paradigm shift Together they produce a coherent, accurate life script

Conclusion: Split Brain Criticized Testing only shows a limited view of functionality of Split Brain patients Simple finding cannot be conclusive because most Split Brain subjects receive surgery because of their epileptic seizures which may have already caused reorganization of brain functions prior to the surgery Patients become over tested because of the small population that have had the surgery Testing become repetitive

Conclusion: New Developments Until recently it has been believed that the entire corpus callosum must be severed to provide proper relief from the severe epilepsy the surgery is trying to negate. However this is not necessarily the case, the corpus callosum might be able to be severed enough to provide relief, without losing all neural integration The back of the corpus callosum (Splenium) is what is usually kept intact Splenium has been found to be the dominant path of the visual aspects of hemispheric integration Makes procedure for severe epilepsy much safer and more practical

Conclusion! Split Brain research has provided important insight into theories of consciousness It is clear that our two hemispheres have separate specializations It remains unclear if consciousness is a function of one hemisphere or a result of the interaction of both

References Churchland, Patricia Smith. Brain-Wise. Massachusetts: Massachusetts Institute of Technology, 2002. Brugger, Peter. From Haunted Brain To Haunted Science. Jefferson: McFarland Press, 2000. Sperry, Roger. 1984. Consciousness, Personal Identity and the Divided Brain. Neuropsychologia, 22(6), p.661-673. Split Brain Consciousness. February 19, 2005. May 22, 2005<http://www.macalester.edu/~psych/whathap/UBNRP/Split_Brain/Split_Brain_Consciousness.html>. Split Brain Behavior. January 7, 2002. May 22, 2005 <http://serendip.brynmawr.edu/bb/neuro/neuro00/web1/Vasiliadis.html>