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






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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

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
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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

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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.661673.
Split Brain Consciousness. February 19, 2005. May 22,
2005<http://www.macalester.edu/~psych/whathap/UBNR
P/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>