SPLIT-BRAIN SURGERY

Elisa Janami

Background

o The corpus callosum is the think band of about 200 million nerve fibres that connect the left and right hemispheres of the brain and was in charge of the transfer of information between these two hemispheres .

Split-Brain surgery is a rare operation for people with certain type of severe epilepsy where the corpus callosum is severed.

Research has shown that the left hemisphere is more involved in verbal processing and the right hemisphere can verbally process information and express it non-verbally.

HEMISPHERIC SPECIALISATION

To understand research findings, we much understand

the specialised functions of each hemisphere of the brain.

Since they work together and share information, this is why patients who undergo Split-Brain surgery are affected.

Further information of hemispheric processing was found by Sperry’s research.

Left hemisphere specialisation

Verbal and analytical functions

Controls right side of the body

Right-hand touch

Processes the right visual field

Language – reading and writing

Rational

Logical

Mathematics and science

Past and present

Cause and effect

Non-verbal functions

Controls left side of the body

Left-hand touch

Processes the left visual field

Symbols and images

Imagination

Creative

Object recognition

Perception and spatial skills

Right hemisphere specialisation

Sperry & Gazzaniga

In the 1960’s Roger Sperry, Michael Gazzaniga and their associates carried out some research for people who suffered a specific kind of epilepsy that had no cure by cutting the corpus callosum, a thick band of about 200 million nerve fibres that connect the left and right hemispheres of the brain. Mr Sperry and his colleagues were interested in the psychological side effects of having two separate brains in one head.

Effects

Language: language processing is mainly handled by the left hemisphere

Visual processing: visual and spatial information is mainly handled by the right hemisphere.

Everyday behaviour is not impacted as much.

Experiment setup

Sperry and Gazzaniga presented a visual image to one side of the visual field for a very brief period (0.1 of a second) so the image was seen by only one half of the retina since there was not enough time for the eye to move.

A set of objects was placed behind a screen so the participant couldn’t see it but could reach it. When the participants were flashed a word, their response and reaction showed the abilities and restrictions of what each hemisphere can process.

(Oxford Psychology Units 3+4, Edwards et al. 2013 Page 202).

Split-brain study 1

(Oxford Psychology Units 3+4, Edwards et al. 2013 Page 202).

Procedure:Words presented to right or left visual field and patients asked to report what they have seen.

Results: - Words presented in the right visual field

(processed in left hemisphere) were read and reported verbally by patients.

- Words presented in the left visual field (processed in the right hemisphere) were not reported verbally by patients. The patients could select the item behind the screen but couldn’t name the object.

From this study we can conclude:- The left hemisphere can identify words and can name them- The right hemisphere can identify words but cannot name them.

Split-brain study 2

(Oxford Psychology Units 3+4, Edwards et al. 2013 Page 203).

Procedure:Words presented to right and left visual field at the same time and patients asked to report what they have seen.

Results: - Words presented in the right visual field (processed in left

hemisphere) were read and reported verbally by patients.

- Words presented in the left visual field (processed in the right hemisphere) were not reported verbally by patients. The patients couldn’t name the the object.

From this study we can conclude:- The left hemisphere can identify words and can name them- The right hemisphere can process words but cannot name them.

Split-brain study 3

(Oxford Psychology Units 3+4, Edwards et al. 2013 Page 203).

Procedure:Image of object presented to right or left visual field and patients asked to report verbally what they have seen and reach under screen and select object.

Results: - When an image, e.g. a hammer, was presented in the left visual field (processed in right

hemisphere) patient couldn’t verbally name object but could grasp the hammer with their left hand. The patient denied seeing anything at all.

- In contrast, when an image, e.g. an apple, was presented on the right visual field (processed in left hemisphere), the patient could easily name it verbally.

From this study we can conclude:- The left hemisphere can identify pictures and can name them- The right hemisphere can identify pictures by touch but cannot name them.- The left hemisphere appears to make the important decisions regarding

presence of an item.

Summary of experiment

When Sperry flashed an image in the left visual field, it is processed in the right hemisphere of the brain so the patient was unable to say what the object was; but they were able to pick it up with his left hand out of a bunch of objects on a desk or could draw a picture of the object with their left hand.

When a picture is presented to the left visual field, it is processed by the non-verbal right hemisphere and cannot be transferred to the other side of the brain where speech is processed in the left hemisphere.

An object presented to the right visual field is processed in the left hemisphere, and since the left hemisphere is the verbal hemisphere, the patients would be able to say it, draw it or pick it up with their right hand.

What happened?

What occurs in Sperry’s experiments is what we have discovered about visual pathways. Each hemisphere is predominantly connected by its contralateral side.

Information presented in the right visual field of each eye falls on the left side of the retina of each eye and goes to the left primary visual cortex in the occipital lobe for processing.

Contralaterally, information presented in the left visual field of each eye falls on the right side of the retina of each eye and goes to the right primary visual cortex in the occipital lobe for processing.

Study Result

Name an object presented to the right visual field

They could name it

Name an object presented to the left visual field

They couldn’t name it

Identify/draw an object presented to the right visual field

They can point to it/draw it with their right hand

Identify/draw an object presented to the left visual field

They can point to it/draw it with their left hand

Conclusions

The Corpus Callosum plays a very important part in allowing visual information to be incorporated with speech.

"The great pleasure and feeling in my right brain is more than my left brain can find the words to tell you."

-Roger Sperry

(Cited in http://www.nobelprize.org/educational/medicine/split-brain/background.html )

Bibliography

http://www.ehow.com/facts_5509980_effects-split-brain-surgery.html

http://marionmoon.hubpages.com/hub/Split-Brain-Surgery

http://www.nobelprize.org/educational/medicine/split-brain/background.html

http://www.psychologytoday.com/blog/the-superhuman-mind/201211/split-brains

http://www.holah.co.uk/study/sperry/

http://en.wikipedia.org/wiki/Split-brain

Oxford Psychology Units 3+4, Edwards et al. 2013

A+ Psych Notes VCE Unit 3, Milesi 2013