Kim Peek, who lent inspiration to the fictional character Raymond Babbitt—played by Dustin Hoffman—in the movie Rain Man, was a remarkable savant. A savant is an individual who—with little or no apparent effort—completes intellectual tasks that would be impossible for ordinary people to master.

Kim Peek’s special abilities started early, around the age of a year and a half. He could read both pages of an open book at once, one page with one eye and the other with the other eye. This style of reading continued until his dead in 2009. His reading comprehension was impressive. He would retain 98 percent of the information he read. Since he spent most of his days in the library with his dad, he quickly made it through thousands of books, encyclopedia and maps. He could read a thick book in an hour and remember just about anything in it. Because he could quickly absorb loads of information and recall it when necessary, his condition made him a living encyclopedia and a walking GPS. He could provide driving directions between almost any two cities in the world. He could also do calendar calculations (“which day was June 15, 1632?”) and remember old baseball scores and a vast amount of musical, historical and political facts. His memory abilities were astounding.

Unlike many individuals with savant syndrome, Kim Peek was not afflicted with autistic spectrum disorder. Though he was strongly introverted, he did not have difficulties with social understanding and communication. The main cause of his remarkable abilities seems to have been the lack of connections between his brain's two hemispheres. An MRI scan revealed an absence of the corpus callosum, the anterior commissure and the hippocampal commissure, the parts of the neurological system that transfer information between hemispheres. In some sense Kim was a natural born split-brain patient.

Split-brain surgery, or corpus calloscotomy, is normally a harsh way of alleviating epileptic seizures, the occurrence of sporadic electrical storms in the brain. The procedure involves severing the corpus callosum, the main fibrous bond between the brain’s left and right hemispheres. After a split-brain surgery the two hemispheres do not exchange information nearly as efficiently as before. This impairment can result in split-brain syndrome, a condition where the separation gives rise to changes in behavior and agency.

Michael Gazzaniga and Roger W. Sperry, the first to study split brains in humans, found that several patients who had undergone a complete calloscotomy suffered from split-brain syndrome. In patients with split-brain syndrome the right hemisphere, which controls the left hand and foot, acts independently of the left hemisphere and the patient’s ability to make rational decisions. This can give rise to a kind of split personality, in which the left hemisphere gives orders that reflect the person’s rational goal, whereas the right hemisphere issues conflicting demands that reveal hidden preferences. One of Gazzaniga and Sperry's patients pulled down his pants with the left hand and back up with the right in a continuing struggle. On a different occasion, this same patient's left hand made an attempt to strike the unsuspecting wife as the right hand grabbed the villainous limb to stop it. Another of their patients, Paul S, had a fully functional language center in both hemispheres. This allowed the researchers to question each side of Paul's brain. When they asked the right side what their patient wanted to be when he grew up, he replied "an automobile racer." When they posed the same question to the left, however, he responded "a draftsman."

Kim Peek is similar to Paul S in this respect. There is no doubt that he must have had a fully developed language-center in both hemispheres. Language is processed in areas of the temporal lobe on the left side of the head. When you read with your left eye, the information first ends up in the right hemisphere and must be transferred to the left hemisphere via the corpus callosum to be processed. This long transfer from one side of the brain to the other is usually a disadvantage. Since Kim Peek didn't have a corpus callosum or a hippocampal commissure, his brain would have had to develop the abilities to process language in both hemispheres. This, of course, gave him a major advantage in terms of speed-reading and information retention. You might think the same would apply to other hemisphere-specific abilities, such as visual imagery and math, which are primarily left-hemisphere based. However, Kim Peek was unable to "reason his way through" mathematical problems. Despite his brilliant mind, his IQ was 87, significantly below normal. It was also difficult for him to follow directions of certain kinds.

There are several respects in which Kim Peek was not like Gazzaniga and Sperry's split-brain patients. He did not exhibit any symptoms of truly split personality or conflicting desires deriving from separate hemispheres. How did he avoid this split in information integration when information could not cross over the three main connections between the hemispheres?

We know that the brain can also transfer information indirectly through subcortical areas. Normally, it is a relatively small amount of information that is transferred that way. But Kim Peek may have developed additional subcortical connections for information transfer.

It's not all animals that have a corpus callosum. Australian Marsupials, such as the kangaroo and the wallaby, are example of creatures that rely heavily on an enlarged anterior commissure or subcortical pathways for information transfer between hemispheres. Kangaroos, wallabies and possums also have a fibrous bundle connecting hemispheres called the fasciculus aberrans.

In Kim Peeks it seems that information that didn't need to travel simply stayed put in the respective hemisphere. At some point, of course, the information would have to be combined to yield a whole. Kim Peek was able to give a full account of any book he read, he didn't give two accounts pertaining of every other page of the books he read. So subcortical connections must have been in charge of hemispheric information transfer.

Peek's ability to retain large amounts of information may have had something to do with another condition he was afflicted with called macrocephaly. This brain abnormality consists in an excessively large head and a correspondingly huge brain. Kim's head was so heavy that it took several years before he could hold it up on his own.

As a baby the real rain man was diagnosed with mental retardation and the physicians told his parents that he never would be able to read or talk. They recommended sending their little boy to a mental institution and getting on with their lives. Despite the recommendation, Kim’s parents chose to raise him at home. They quickly realized that their little boy with the oversized head had a remarkable brain. Due to his parents' efforts, Kim had the opportunity to develop his amazing talents. A large head does not equal intelligence or ability to retain information. But it does provide more storage space for someone who is able to process the content of 10,000 books, which was the number of books Peek had read by the time of the his death in 2009.

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