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Split Brain Split Brain

Consciousness Consciousness

Trevor Norlock Trevor Norlock Daniel Bowling Daniel Bowling Adrienne Keener Adrienne Keener

Dina Saab Dina Saab

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Introduction Introduction

 In a Healthy brain, stimuli is In a Healthy brain, stimuli is

communicated between the two communicated between the two

hemispheres via the corpus callosum hemispheres via the corpus callosum

 When this is severed, a split brain exists When 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 callosum

to the other hemi via the corpus callosum

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Introduction Introduction

 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

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History History

 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.

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History History

 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 epilepsy

epilepsy

 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.

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History History

 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

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History History

 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 "tooth right hand, the patient will immediately say "tooth

brush"

brush"

(8)

History History

 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

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Implications for Theories of Implications for Theories of

Consciousness Consciousness

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

regarding 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?

(10)

Mental Duality Hypothesis Mental 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 detected

so the duality is not detected

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Split Brain and Consciousness Split 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 actions motor actions

 Ex: Gazzaniga’s chicken claw snowy scene Ex: Gazzaniga’s chicken claw snowy scene experiment

experiment

 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 ground

hand 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 consciousness

hemispheres have independent consciousness

(12)

Global Hypothesis Global 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 hemispheres

hemispheres

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

(13)

The Intact Brain and The Intact Brain and

Consciousness Consciousness

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

different strategies for dealing with information

information

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

of the functions of both hemispheres

(14)

Associative Processing Associative Processing

 Semantic Networks Semantic Networks

Spreading

Activation theory

Evidence:

Semantic Priming Effect – Faster

responses when 2 words are

semantically

(15)

Interpretation Strategies Interpretation Strategies

 Lateralized semantic priming tasks have Lateralized semantic priming tasks have revealed that:

revealed that:

 LH LH : Narrow spread of semantic activation : Narrow spread of semantic activation

 Better for making close associations Better 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 old

allows integration of new info with old

 RH RH : Diffuse spread of semantic activation : Diffuse spread of semantic activation

 Better for making remote associations Better for making remote associations

 Promotes creative, new and uncommon Promotes creative, new and uncommon associations

associations

(16)

Evidence for Different strategies Evidence 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

Hemisphere Hemisphere

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

preferentially processed by the Right Hemisphere

Hemisphere

(17)

Finding Patterns Finding 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”

(18)

Interpreters Interpreters

 LH LH : Involved in preserving the current : Involved in preserving the current paradigm and suppressing opposing paradigm and suppressing opposing

evidence evidence

 RH RH : Detecting anomalies and trying to : Detecting anomalies and trying to force a paradigm shift

force a paradigm shift

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

accurate life script

(19)

Conclusion: Split Brain Criticized Conclusion: Split Brain Criticized

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

of 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 surgery functions prior to the surgery

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

 Testing become repetitive Testing become repetitive

(20)

Conclusion: New Developments Conclusion: 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 integration relief, 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 intact

usually 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 integration

visual aspects of hemispheric integration

Makes procedure for severe epilepsy much safer and Makes procedure for severe epilepsy much safer and

(21)

Conclusion!

Conclusion!

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

consciousness consciousness

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

separate 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 both

the interaction of both

(22)

References References

Churchland, Patricia Smith. Churchland, Patricia Smith. Brain-Wise Brain-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 Science

Science . 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/UBNR 2005<http://www.macalester.edu/~psych/whathap/UBNR

P/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>

References

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