simple explanations of interesting brain conditions

The Spooky Story of the Split-brain

You’ve likely heard something about the logical left brain vs. the creative right. It’s reasonable to say that most experts would agree this is an outdated, oversimplified view of the reality. It isn’t so much that emotion or rationality are specifically housed on either side as it is that some functions tend to be more dominant in one hemisphere, with constant communication occurring throughout.  Recent discoveries in neuroplasticity only complicate these concepts further; we now know that some functions of the brain can be transferred to other areas, sometimes due to brain injury but even as the adaptive result of normal experiences. So, what would happen if someone were to have their left and right hemispheres disconnected? Well my friend, tighten that seat belt, because science truly is stranger than fiction.

Corpus Callosectomy

In the 1940s American neurosurgeon Dr. William P. van Wagenen (1897-1961) began conducting the corpus callosectomy as a treatment for severe epilepsy; the surgery involves cutting through the corpus callosum, the main link between the two halves of the brain. The surgery was very successful in ending epileptic seizures, and patients seemed to recover fairly regularly. It was not until the 50s and 60s that Roger Sperry (1913-1994) and Michael Gazzaniga (1939) began investigating the implications of this procedure. The results of these studies would go on to become legendary, earning Sperry the 1981 Nobel Prize in Physiology and Medicine.


To understand these findings we must first grasp two basic neurological facts. As mentioned earlier, each half of the brain tends to dominate certain functions. In this case the important detail is that speech-control is usually situated on the left side of the brain, meaning that this hemisphere has a monopoly on verbal communication. The second important thing we must understand is that the left hemisphere tends to control the right side of our body, while the right hemisphere controls the left.

Scientific American Frontier: Season 7, Episode 3 – Pieces of Mind (1997)

Now we are prepared to move onto Sperry and Gazzaniga’s fascinating, disturbing results. What they discovered was that each hemisphere, now acting largely independently, began to develop their own perceptions and impulses. Some split-brain patients report that their left hand would sometimes pull down their pants while the other put them on, or put things into their shopping cart while the other took them out. Is the right hemisphere a prisoner in there, forced to go along with the narrative of the vocal left? In the above video Gazzaniga shares some pretty strange examples with split-brain patient Joe. Notice how Joe seems to confabulate in the same way patients did from the previous article on Anton-Babinski syndrome?

Agenesis of the Corpus Callosum

Rather unsettling how the brain will react when you split it in two isn’t it? but what if there was never a link in the first place? Agenesis of the corpus callosum (ACC) is a rare birth defect where a person is born with an underdeveloped or absent corpus callosum. The effects of this vary; delayed development, cognitive disability and social difficulties are amongst the most common. Perhaps the most famous patient with ACC was Laurence Kim Peek (1951 – 2009), sometimes known as the Rain Man. This incredible character was what they call a megasavant; from an early age he displayed an astronomical memory yet this came at the price of rather extreme social difficulties. Peek read books by scanning the left page with his left eye and the right page with his right eye, finishing pages in 8-10 seconds and remembering 98% of everything he read. They say he could recall the contents of over 12,000 books, and was an expert on a range of subjects.

Real Stories: The Boy with the Incredible Brain (2005)

Interestingly there was never evidence of Peek experiencing a rogue limb, or any actions that he could not explain for that matter. This was likely due to the fact that he had developed language centers in both hemispheres of the brain; both had the ability to vocally explain their actions. Does this mean that sometimes you would be talking to his right hemisphere and sometimes his left? Perhaps his brain, unlike Gazzaniga’s patients, was somehow capable of transferring information efficiently without the corpus callosum. We will never know, Peek died in his home in 2009, aged 58.

Wrapping This Thing Up

The split-brain phenomenon, through either surgery or birth, certainly has a lot to teach us about the mind and brain. Delving into the subject leads down all sorts of rabbit-holes involving consciousness, identity and the self. Indeed most of us find the idea of tinkering with our most personal machinery pretty alarming, yet believe it or not they are still performing corpus callosectomy on rare occasions. I’ll leave you with one last video to ponder, just to mess with you a little bit more:

The Science Network: Beyond Belief – Session 4 (2006)


All images produced by the author unless otherwise specified.

  1. Wright, J. J. (2016). Work Toward a Theory of Brain Function (Thesis, Doctor of Science). University of Otago. Retrieved from
  2. Gazzaniga. M. (2003) The Split-brain: Rooting consciousness in biology. doi:10.1073/pnas.1417892111

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