Split Brain Split Brain ConsciousnessConsciousness

Trevor NorlockTrevor NorlockDaniel BowlingDaniel Bowling

Adrienne KeenerAdrienne KeenerDina SaabDina Saab

IntroductionIntroduction

In a Healthy brain, stimuli is In a Healthy brain, stimuli is communicated between the two communicated between the two hemispheres via the corpus callosumhemispheres via the corpus callosum

When this is severed, a split brain existsWhen this is severed, a split brain exists Epilepsy-Epilepsy- Seizures trigger massive Seizures trigger massive

neuron activation in one hemi, that travels neuron activation in one hemi, that travels to the other hemi via the corpus callosumto the other hemi via the corpus callosum

IntroductionIntroduction To prevent these seizures, neurosurgeons can To prevent these seizures, neurosurgeons can

perform a commissurotomy perform a commissurotomy The surgeon opens the skull, lays back the The surgeon opens the skull, lays back the

brain's coverings and, with a tool called a brain's coverings and, with a tool called a cerebral retractor, exposes the corpus callosum cerebral retractor, exposes the corpus callosum between the two hemispheres between the two hemispheres

The doctor snips through the corpus callosum, The doctor snips through the corpus callosum, severing communication between the severing communication between the hemispheres and preventing the transfer of hemispheres and preventing the transfer of seizures seizures

HistoryHistory

The "split brain" was first discovered in the The "split brain" was first discovered in the laboratory by Roger Sperry and Ronald laboratory by Roger Sperry and Ronald Meyers Meyers

Initially they began experimenting with Initially they began experimenting with cats, and later proceeded to study cats, and later proceeded to study monkeys monkeys

In 1961 the first human patient was In 1961 the first human patient was subject to the split brain surgery. subject to the split brain surgery.

HistoryHistory

The procedure worked well as a "cure" for The procedure worked well as a "cure" for patients who suffered from severe patients who suffered from severe epilepsyepilepsy

Patients were not able to communicate Patients were not able to communicate information from one hemisphere to the information from one hemisphere to the other, other, almost as though they now had two almost as though they now had two separate brains.separate brains.

HistoryHistory How (and what) the hemispheres How (and what) the hemispheres

communicate would provide valuable communicate would provide valuable insight into the insight into the "mind""mind" of a split brain of a split brain patient patient

How did a commissurotomy affect one's How did a commissurotomy affect one's perceptions of the outside world? perceptions of the outside world?

Interestingly enough, the centers for Interestingly enough, the centers for speech interpretation and production are speech interpretation and production are located in the left hemisphere located in the left hemisphere

HistoryHistory Similarly, if the patient is blindfolded and a Similarly, if the patient is blindfolded and a

familiar object, such as a toothbrush, is placed in familiar object, such as a toothbrush, is placed in his left hand, he appears to know what it is; for his left hand, he appears to know what it is; for example by making the gesture of brushing his example by making the gesture of brushing his teeth. teeth.

But he cannot name the object to the But he cannot name the object to the experimenter experimenter

If asked what he is doing with the object, If asked what he is doing with the object, gesturing a brushing motion, he has no idea gesturing a brushing motion, he has no idea

But if the left hand gives the toothbrush to the But if the left hand gives the toothbrush to the right hand, the patient will immediately say right hand, the patient will immediately say "tooth brush" "tooth brush"

HistoryHistory Micheal Gazzaniga, who did his graduate work Micheal Gazzaniga, who did his graduate work

in Sperry's laboratory, did further experiments in Sperry's laboratory, did further experiments which showed the attempts of the left which showed the attempts of the left hemisphere to compensate for it's lack of hemisphere to compensate for it's lack of information, as well as attempts by the right information, as well as attempts by the right hemisphere to get it's knowledge conveyed hemisphere to get it's knowledge conveyed

The idea of an ‘interpreter”The idea of an ‘interpreter” These experiments provided insight into the These experiments provided insight into the

functioning's of the two hemispheres and how functioning's of the two hemispheres and how they are different they are different

Implications for Theories of Implications for Theories of ConsciousnessConsciousness

Split brain research has sparked questions Split brain research has sparked questions regarding human conscious experienceregarding human conscious experience

Is consciousness a function of one or both Is consciousness a function of one or both hemispheres?hemispheres?

What role does each hemisphere play in What role does each hemisphere play in conscious experience?conscious experience?

Do split brain patients exhibit different behavioral Do split brain patients exhibit different behavioral patterns compared to normals?patterns compared to normals?

Is the consciousness of split brain patients Is the consciousness of split brain patients different than normals?different than normals?

Mental Duality HypothesisMental Duality Hypothesis

Each hemisphere has a separate Each hemisphere has a separate consciousness. The function of the corpus consciousness. The function of the corpus callosum is duplicative rather than callosum is duplicative rather than integrative. (Puccetti)integrative. (Puccetti)

In the intact brain the conscious In the intact brain the conscious experiences of the two hemispheres are experiences of the two hemispheres are kept in synchrony by the corpus callosum, kept in synchrony by the corpus callosum, so the duality is not detectedso the duality is not detected

Split Brain and ConsciousnessSplit Brain and Consciousness Experiments conducted on split brain subjects Experiments conducted on split brain subjects

have shown that each hemisphere can have shown that each hemisphere can independently perceive stimuli and execute independently perceive stimuli and execute motor actionsmotor actions

Ex: Gazzaniga’s chicken claw snowy scene Ex: Gazzaniga’s chicken claw snowy scene experimentexperiment

Ex: Right hand picks up paper to read and left Ex: Right hand picks up paper to read and left hand takes it and throws it on the groundhand takes it and throws it on the ground

This does not necessarily imply that the two This does not necessarily imply that the two hemispheres have independent consciousnesshemispheres have independent consciousness

Global HypothesisGlobal Hypothesis Consciousness in the intact brain is an emergent Consciousness in the intact brain is an emergent

result of the interaction between the two result of the interaction between the two hemisphereshemispheres

The corpus callosum serves to integrate the The corpus callosum serves to integrate the lateralized functions of the two hemisphereslateralized functions of the two hemispheres

In the split brain, unified conscious experience is In the split brain, unified conscious experience is maintained by interhemispheric subcortical maintained by interhemispheric subcortical connections and various bilateral connections and various bilateral representations (Sperry)representations (Sperry)

The Intact Brain and The Intact Brain and ConsciousnessConsciousness

The Left and Right hemispheres have The Left and Right hemispheres have different strategies for dealing with different strategies for dealing with informationinformation

Our conscious experience is an integration Our conscious experience is an integration of the functions of both hemispheresof the functions of both hemispheres

Associative ProcessingAssociative Processing

Semantic Networks Semantic Networks Spreading Activation theory

Evidence: Semantic Priming Effect – Faster responses when 2 words are semantically related then when they are not

Interpretation StrategiesInterpretation Strategies Lateralized semantic priming tasks have Lateralized semantic priming tasks have

revealed that:revealed that: LHLH: Narrow spread of semantic activation: Narrow spread of semantic activation Better for making close associationsBetter for making close associations Protects the spread from going too far and Protects the spread from going too far and

allows integration of new info with oldallows integration of new info with old RHRH: Diffuse spread of semantic activation: Diffuse spread of semantic activation Better for making remote associationsBetter for making remote associations Promotes creative, new and uncommon Promotes creative, new and uncommon

associationsassociations

Evidence for Different strategiesEvidence for Different strategies

Electrophysiological studies provide Electrophysiological studies provide evidence that:evidence that:

Close prototypical associations are Close prototypical associations are preferentially processed by the Left preferentially processed by the Left HemisphereHemisphere

Remote, less prototypical associations are Remote, less prototypical associations are preferentially processed by the Right preferentially processed by the Right HemisphereHemisphere

Finding PatternsFinding Patterns

When perceiving patterns in data we are When perceiving patterns in data we are prone to making the following types of prone to making the following types of errors:errors:

TYPE I: Perceiving a pattern where none TYPE I: Perceiving a pattern where none exists “False Alarm”exists “False Alarm”

TYPE II: Not perceiving a pattern where TYPE II: Not perceiving a pattern where one exists “Miss”one exists “Miss”

InterpretersInterpreters

LHLH: Involved in preserving the current : Involved in preserving the current paradigm and suppressing opposing paradigm and suppressing opposing evidence evidence

RHRH: Detecting anomalies and trying to : Detecting anomalies and trying to force a paradigm shiftforce a paradigm shift

Together they produce a coherent, Together they produce a coherent, accurate life scriptaccurate life script

Conclusion: Split Brain CriticizedConclusion: Split Brain Criticized

Testing only shows a limited view of functionality Testing only shows a limited view of functionality of Split Brain patientsof Split Brain patients

Simple finding cannot be conclusive because Simple finding cannot be conclusive because most Split Brain subjects receive surgery most Split Brain subjects receive surgery because of their epileptic seizures which may because of their epileptic seizures which may have already caused reorganization of brain have already caused reorganization of brain functions prior to the surgeryfunctions prior to the surgery

Patients become over tested because of the Patients become over tested because of the small population that have had the surgerysmall population that have had the surgery

Testing become repetitiveTesting become repetitive

Conclusion: New DevelopmentsConclusion: New Developments Until recently it has been believed that the entire corpus Until recently it has been believed that the entire corpus

callosum must be severed to provide proper relief from callosum must be severed to provide proper relief from the severe epilepsy the surgery is trying to negate. the severe epilepsy the surgery is trying to negate.

However this is not necessarily the case, the corpus However this is not necessarily the case, the corpus callosum might be able to be severed enough to provide callosum might be able to be severed enough to provide relief, without losing all neural integrationrelief, without losing all neural integration

The back of the corpus callosum (Splenium) is what is The back of the corpus callosum (Splenium) is what is usually kept intactusually kept intact

Splenium has been found to be the dominant path of the Splenium has been found to be the dominant path of the visual aspects of hemispheric integrationvisual aspects of hemispheric integration

Makes procedure for severe epilepsy much safer and Makes procedure for severe epilepsy much safer and more practicalmore practical

Conclusion!Conclusion!

Split Brain research has provided Split Brain research has provided important insight into theories of important insight into theories of consciousnessconsciousness

It is clear that our two hemispheres have It is clear that our two hemispheres have separate specializationsseparate specializations

It remains unclear if consciousness is a It remains unclear if consciousness is a function of one hemisphere or a result of function of one hemisphere or a result of the interaction of boththe interaction of both

References References Churchland, Patricia Smith. Churchland, Patricia Smith. Brain-WiseBrain-Wise. Massachusetts: . Massachusetts:

Massachusetts Institute of Technology, 2002. Massachusetts Institute of Technology, 2002. Brugger, Peter. Brugger, Peter. From Haunted Brain To Haunted From Haunted Brain To Haunted

ScienceScience. Jefferson: McFarland Press, 2000.. Jefferson: McFarland Press, 2000. Sperry, Roger. 1984. Consciousness, Personal Identity Sperry, Roger. 1984. Consciousness, Personal Identity

and the Divided Brain. and the Divided Brain. Neuropsychologia, 22(6),Neuropsychologia, 22(6), p.661- p.661-673.673.

Split Brain Consciousness. February 19, 2005. May 22, Split Brain Consciousness. February 19, 2005. May 22, 2005<http://www.macalester.edu/~psych/whathap/UBNR2005<http://www.macalester.edu/~psych/whathap/UBNRP/Split_Brain/Split_Brain_Consciousness.html>.P/Split_Brain/Split_Brain_Consciousness.html>.

Split Brain Behavior. January 7, 2002. May 22, 2005 Split Brain Behavior. January 7, 2002. May 22, 2005 <http://serendip.brynmawr.edu/bb/neuro/neuro00/web1/<http://serendip.brynmawr.edu/bb/neuro/neuro00/web1/Vasiliadis.html>Vasiliadis.html>