The "split brain" and Roger Wolcott Sperry were the subjects of Split Brain Experiments.
The brains of cats, monkeys, and humans were used to study functional differences between the two hemispheres of the brain in the United States.The corpus callosum is a large bundle of neurons that connect the two hemispheres of the brain.The function of each side of the brain was studied by Sperry.He found that if the hemispheres were not connected, they wouldn't work together.Animals were able to memorize double the information because of the split-brain.The idea was tested in humans with their corpus callosum severed as treatment for a seizure disorder.The human brain has different functions.The left hemisphere is better at interpreting language than the right.The split-brain research done by Sperry earned him a share of the 1981 Nobel Prize in Physiology or Medicine.
In the 1940s and 1950s, Sperry studied other aspects of brain function and connections in mammals and humans.The axons, the long fiber-like process of brain cells, connected to their target organs with special chemical markers.A set of individual nerves could develop into a complex nervous system.The brain patterns of animals were studied by Sperry.His research on the split-brain was done at Caltech in Pasadena, California, where he moved in 1954.
In the late 1950s, Sperry began his research on split-brain.Even though the hemispheres of the severed humans could not communicate, they did not show any significant difference in function.There should be major consequences from cutting the brain structure as it must have an important function.Experiments were designed to document the effects of a severed callosum.He knew that the right and left hemispheres of the brain were responsible for movement and vision on the opposite side.Sperry designed experiments in which he could carefully monitor what each eye saw and what information was going to each hemisphere.
There were experiments with cats, monkeys, and humans.The split-brain cats were the beginning of his experiments.He presented them with two different blocks, one of which had food under it.He put the food under the other block after changing the eye patch on the cat.The cat could not distinguish between the blocks with both eyes.The monkeys were made to use both eyes at the same time, which was possible due to special projectors and light filters.The split-brain monkeys were able to memorize two scenarios at the same time.The hemispheres can't communicate with each other because of a severed callosum.
The human volunteers had a severed callosum.When he showed a word to one of the eyes, he found that split-brain people could only remember it with their right eye.Sperry showed the participants two different objects, one to their left eye only and the other to the right eye, and then asked them to draw what they saw.All participants described what they saw with their right and left eyes.The left hemisphere of the brain was better at analyzing speech than the right.
The idea that one hemisphere of the brain is better at performing some functions than the other hemisphere was studied in the 1960s by multiple scientists.Researchers didn't know which side of the brain was responsible for which tasks.
The article "Cerebral Organization and Behavior" was published in 1961.To test how the cutting of the corpus callosum affected mammals, Sperry had multiple cats perform tasks that involved their vision and response to a visual stimuli.He covered one of the cat's eyes to keep an eye on it.If he wanted the cat to use one eye, he could switch the eye patch from one to the other.The cats were shown two wooden blocks with different designs.The cat was under one of the blocks.He told the cats that when they saw the blocks with one eye, the food was under the circle block, while the other saw it with a cross.The cats were taught by Sperry to move the wooden block away from the two objects with their paws.
When the eye patch was removed, the cats could see with both eyes.When the cats could use both eyes, they hesitated and then chose the blocks that were closest to each other.The left and right hemispheres are connected by the right eye.The hemispheres could not communicate because of the cut to the callosum.If the hemispheres couldn't communicate and the information from one eye only went to one hemisphere, the other hemisphere would remember which block had food under it.The cats remembered two different scenarios with different hemispheres.He suspected that the cats had two different brains, as their hemispheres could not interact and act as if the other did not exist.
In an experiment with monkeys, he cut their corpus callosum.He wanted to see if both hemispheres could operate at the same time.It required separation of visual fields, or making sure that the right eye saw a circle, but without an eye patch and both eyes would see something at the same time.It was solved by using two projectors that were positioned side-by-side at an angle.The projector on the right showed a circle with a cross on it, while the projector in the left showed the same.The light filters were placed in front of the monkey's eyes.Each eye was able to see the images from only one projector because of the light filters.One of the eyes was able to see the circle on the right, while the other saw the cross in the left.Sperry made the monkeys memorize two different scenarios at the same time because he knew there was no sharing of information between the right and left hemispheres.
The left eye saw a scenario in which food would be dispersed when the monkey pressed a button with a cross on it.It was the same button, but the eyes saw it differently because of two projectors and special light filters.The brain was learning two different problems at the same time.The assumption that the hemispheres were not communicating and each one was acting as the only brain was supported by the fact that split-brain monkeys learned two problems in the time it would take a normal monkey to learn one.There were drawbacks to the procedure, and that seemed to be a benefit.
The next set of experiments was performed on human volunteers who had their corpus callosum severed due to outside factors.Volunteers were asked to do multiple tests.The opposite hemisphere of the brain would only analyze information from one eye and the hemispheres would not be able to communicate with each other.The participants were asked to look at a white screen with a black dot in the middle.The black dot was the dividing point for the fields of view for a person, so the right hemisphere of the brain analyzed everything to the left of it.Sperry asked the participants to tell him what they saw after he showed them a word on one side of the black dot.The left hemisphere of the brain analyzed what the participants saw when they saw the word with their right eye.The participants could not remember what the word was if they saw it with their left eye.The left hemisphere could articulate language, while the right could not.
The function of the right hemisphere was tested by Sperry.He asked the participants of the experiment if they could not remember the word because it was in the left visual field to close their eyes and draw the object with their left hand.People can draw pictures of words they see and recognize them.If he showed the word to the same visual field twice, the person would recognize it as a word they've seen before, but if he show it to different visual fields, they wouldn't know.The left hemisphere was responsible for understanding and remembering the language, while the right hemisphere couldn't articulate it.It was known that the language center was in the left hemisphere.
The ability of the right hemisphere to recognize words was studied by Sperry.Volunteers were asked to put their left hand into a box with different tools that they couldn't see.The participants saw a word that described one of the objects in the box in their left field of view.Most participants picked up the needed object from the box without seeing it, but if Sperry asked them for the name of the object, they could not say it and they did not know why they were holding that object.The right hemisphere had some language recognition ability, but it could not say a word, so the person wouldn't be able to say what it was.