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"Understanding the Brain", The Birth of a Learning Science, 2007, page 115
“Is There One ‘Left-Brain’ & Another ‘Right-Brain’?” (3)
The 60s, Studying the “Split Brain Alive”
The 60s, Studying the “Split Brain Alive”
Until the 1960s, methods for observing the dominant role of the left hemisphere in language use and processing (lateralisation of language) were based on studies postmortem of patients with brain lesions. Some neurologists nevertheless claimed that language might not be entirely a left hemisphere function in that it was impossible to conclude no role for the right hemisphere on the basis of lack of lesions there among those who had had language impairments. Lesions only on the left side could be random.
The pertinence of this intuition was underlined by studies carried out on “split-brain” patients.
The corpus callosum of these patients was severed in order to stop epileptic attacks from one hemisphere to the other.
While the primary goal of the operation was to reduce epileptic fits, it also allowed researchers to study the role of each hemisphere on these patients.
The first such studies were conducted in the 1960s and 1970s, with Medicine Nobel Prize winner Roger Sperry and his team from the California Institute of Technology playing a dominant role.
They succeeded in supplying information to a single hemisphere in their “split-brain” patients and asked them to use each hand separately to identify objects without looking at them.
This experimental protocol built on the fact that basic sensory and motor functions are symmetrically divided between the two hemispheres of the brain - the left hemisphere receives almost all sensory information from and controls movements to the right part of the body and vice versa.
Sensory information from the right hand is received in the left hemisphere and that from the left hand in the right hemisphere.
When patients touched an object with their right hand, they could easily name the object but not when they touched it with the left hand. Here was proof that the left hemisphere is the seat of principal language functions.
This unequal localisation of language functions created the idea of the left hemisphere as the verbal one and the right hemisphere as the non-verbal one. Since language has often been perceived as the noblest function of the human species, the left hemisphere was declared “Dominant".
Other experiments with the same type of patients helped to clarify the role of the right hemisphere. A video made by Sperry and Gazzaniga about the split-brain patient W.J. gives a surprising demonstration of the superiority of the right hemisphere for spatial vision. The patient was given several dice, each with two red sides, two white sides, and two sides with alternating white and red diagonal stripes. The task of the patient was to arrange the dice according to patterns presented on cards. The beginning of the video shows W.J. quickly arranging the dice in the required pattern using his left hand (controlled, remember, by the right hemisphere). He had great difficulty, however, completing the same task using his right hand – he was slow and moved the dice indecisively. Once his left hand intervenes, he became quick and precise but when the researchers hold it back he again became indecisive.
Other research by Roger Sperry et al. (1969) confirmed the domination of the right hemisphere in spatial vision. This role was then confirmed by clinical case studies. Patients suffering from lesions in the right hemisphere were not able to recognise familiar faces; other patients had difficulty with spatial orientation.
Some patients with lesions in the right hemisphere have shown defects in identifying the emotional intonation of words and in recognising emotional facial expressions. Behavioural studies back up the clinical studies: speech rhythms are best perceived when the sounds are received by the left ear so that the information goes to the right hemisphere and images seen by the left visual field provoke greater emotional reaction. It was deduced from this that the right hemisphere was also specialised in the processes related to emotions.
The pertinence of this intuition was underlined by studies carried out on “split-brain” patients.
The corpus callosum of these patients was severed in order to stop epileptic attacks from one hemisphere to the other.
While the primary goal of the operation was to reduce epileptic fits, it also allowed researchers to study the role of each hemisphere on these patients.
The first such studies were conducted in the 1960s and 1970s, with Medicine Nobel Prize winner Roger Sperry and his team from the California Institute of Technology playing a dominant role.
They succeeded in supplying information to a single hemisphere in their “split-brain” patients and asked them to use each hand separately to identify objects without looking at them.
This experimental protocol built on the fact that basic sensory and motor functions are symmetrically divided between the two hemispheres of the brain - the left hemisphere receives almost all sensory information from and controls movements to the right part of the body and vice versa.
Sensory information from the right hand is received in the left hemisphere and that from the left hand in the right hemisphere.When patients touched an object with their right hand, they could easily name the object but not when they touched it with the left hand. Here was proof that the left hemisphere is the seat of principal language functions.
This unequal localisation of language functions created the idea of the left hemisphere as the verbal one and the right hemisphere as the non-verbal one. Since language has often been perceived as the noblest function of the human species, the left hemisphere was declared “Dominant".
Other experiments with the same type of patients helped to clarify the role of the right hemisphere. A video made by Sperry and Gazzaniga about the split-brain patient W.J. gives a surprising demonstration of the superiority of the right hemisphere for spatial vision. The patient was given several dice, each with two red sides, two white sides, and two sides with alternating white and red diagonal stripes. The task of the patient was to arrange the dice according to patterns presented on cards. The beginning of the video shows W.J. quickly arranging the dice in the required pattern using his left hand (controlled, remember, by the right hemisphere). He had great difficulty, however, completing the same task using his right hand – he was slow and moved the dice indecisively. Once his left hand intervenes, he became quick and precise but when the researchers hold it back he again became indecisive.
Other research by Roger Sperry et al. (1969) confirmed the domination of the right hemisphere in spatial vision. This role was then confirmed by clinical case studies. Patients suffering from lesions in the right hemisphere were not able to recognise familiar faces; other patients had difficulty with spatial orientation.Some patients with lesions in the right hemisphere have shown defects in identifying the emotional intonation of words and in recognising emotional facial expressions. Behavioural studies back up the clinical studies: speech rhythms are best perceived when the sounds are received by the left ear so that the information goes to the right hemisphere and images seen by the left visual field provoke greater emotional reaction. It was deduced from this that the right hemisphere was also specialised in the processes related to emotions.
"Understanding the Brain", The Birth of a Learning Science, 2007, page 115
(To be continued...)
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