Split Brain Split Brain
Consciousness Consciousness
Trevor Norlock Trevor Norlock Daniel Bowling Daniel Bowling Adrienne Keener Adrienne Keener
Dina Saab Dina Saab
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
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
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.
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.
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
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"
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
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?
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
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
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)
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
Associative Processing Associative Processing
Semantic Networks Semantic Networks
Spreading
Activation theory
Evidence:
Semantic Priming Effect – Faster
responses when 2 words are
semantically
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
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
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”
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
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
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
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
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>.
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