What happens when you split your brain

What happens when you split your brain in the middle? i-ead20e5fec1c13ae3d9a734842349e45-openclipart_brain.png By splitting I mean the surgical kind where the corpus callosum (the connecting neural tissue between right and left hemispheres) is severed. Why would anyone do that, I hear you scream. Well, there are instances when this may be the only possible option for someone to survive their ailment (like severe epileptic seizures).

Back to the question. So, what happens? Back in 1950s Nobel laureate Roger Sperry assisted by his colleagues and his able protege Michael Gazzaniga tested a patient - before his brain was split and after his brain was split -, for cognitive functions. The operation was done and it seemed to have worked (and the patient survived too). So, imagine the researchers' astonishment when they tested the patient after the cut-up.

Here's how one of the tests went (I am embellishing it somewhat): They masked the patient's Left eye and flashed an apple to the Right eye. The patient said "An apple". Then, they masked the Right eye and flashed an apple to the Left eye. The patient said nothing. Did you see anything? No, nothing. Are you messing with us? No, am not.

Keeping his Right eye still masked, they placed a basket within reach of his left hand with apples and oranges. Can you pull the thing you didn't see from the basket on the left? Without a word he pulls an apple out and hands it over.

Holy smokes! What just happened here!

That's when it hit the researchers that the Left brain controls the right side of the body and the Right brain controls the left side [Update: I could be wrong. See Mo's comment below]. Moreover, the Right brain cannot talk - although it can direct the left hand to grab what the left eye saw. Are there two people in everyone's head constantly consulting about how to deal with the world? If we split the brain are we also irrevocably splitting the mask that hides two faces inside? These questions are, naturally, much more deeper and interesting than what I can convey. However, I wanted to capture the amazing revelation this was to me when I learnt it.

More to read
-Nobel Prize Lecture of Roger Sperry
-All In The Mind - An illuminating Interview with Michael Gazzaniga
-Seed Salon Conversation between Tom Wolfe and Michael Gazzaniga [video. thanks, Mo, JM]

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One thing I have never heard is, can the knowledge learned on one side of the brain after splitting be understood by the other? Is there ANY communication, however indirect, between them?

By Old Bogus (not verified) on 01 Jul 2008 #permalink

As a programmer, I have often faced the situation where right-brain-me writes some fancy code, and left-brain-me does not understand it and has to be reassured that it really will work. The reassurance is sort of a wordless "yes, I checked it and it's ok, I promise".

Most recent time this happened was with some thread synchronisation java code - any number of threads can read, but if any thread wants to write then it acquires an exclusive lock, meaning that it has to wait till all readers are done. Left-brain-me writing this is still not 100% sure that it provably works, but I wrote a test to throw a few dozen working threads at it for 30 seconds, and it didn't break.

When I'm flowing, coding is a rapid interplay of the two quite different modes of thinking.

By Paul Murray (not verified) on 01 Jul 2008 #permalink

Nitpick: right and left visual fields, not right and left eyes.

I can't help but wonder what kinds of identity issues split-brain patients have. Is it even physically possible for them to be one identity any longer? And, given that they don't seem to complain of suddenly feeling like two people, does one hemisphere take over, or was one hemisphere already dominant, or what? (The idea of "identity" being localized to one or the other hemisphere is really distasteful.)

Also, a slightly less deep question: how do they do things that require the synchronous action of two hands? Visual feedback? How much trouble do they have with this?

Neat stuff.
Stanislaw Lem wrote an cool novel story where a man's (Ijon Tichy) corpus callosum is severed, called "Peace on Earth"

There are some interesting (thought) experiments described in there...

Gazzaniga is interviewed by Tom Wolfe in the current issue of Seed.

By the way, I think contralateral control had already long been known from ablation studies in animals.

"Are there two people in everyone's head constantly consulting about how to deal with the world? "

See "The Origin of Conciousness in the Breakdown of the Bicameral Mind" - Julian Jaynes.

A book that is almost certainly wrong in almost every respect, but has the grain of a very special idea - yes, there might just be two people in there, and the negotiation between the two halves might just explain our concious selves.

Breifly, the idea is that the two halves of the human brain originally formed separate operational units that co-operated unconciously (mostly via senses watching what the other was doing) and conciousness was a response to a crisis when each half of the brain started to specialize. Jaynes goes off into whacko territory when he places this crisis in historical times- ie. between the formation of language and writing.

The idea has a bit of plausibility, but the timescale seems much too short.

Great read anyway and quite thought provoking. My favorite gonzo book title as well.

(I'll have to put it on my Intimidation Bookshelf at work - containing the books I want you to notice so you don't tangle with me on more mundane issues. Right alongside "The Mathematical Foundations of Quantum Physics" - J. von Neumann)

One thing I have never heard is, can the knowledge learned on one side of the brain after splitting be understood by the other? Is there ANY communication, however indirect, between them?

The corpus callosum isn't the only white matter bundle communicating between the hemispheres. There are the anterior and posterior commissures, some communication through the fornix, and a cerebellar commissure, for example.

By Epinephrine (not verified) on 03 Jul 2008 #permalink

Stanislaw Lem wrote an cool novel story where a mans (Ijon Tichy) corpus callosum is severed, called "Peace on Earth"

Not only that, Lem even explicitly quoted Michael Gazzaniga (something from 'The Bisected Brain').

Thanks for this post, especially the last paragraph. This subject was quite a revelation to me too, especially the implication that having "two minds" was a possibility.

This is a video that features Dr. Jill Bolte Taylor, a "Harvard trained neuroanatomist" who suffered a massive stroke which, essentially, shut down her entire left hemisphere. She was featured in the NY Times and has a long interview with Oprah.
http://www.youtube.com/watch?v=UyyjU8fzEYU

Granted, the presentation gets a bit evangelistic, but even that is interesting, given her training, and primary interest in studying brain phenomena.

I am not sure there are two people inside our brains so much as there are two profoundly different ways of processing information, and experiencing "reality." The left side seems (according to Dr. Taylor) to monopolize most of our senses of reality (linear time, logic, "stories" that tie events together) whereas that "intuitive" feeling that arises from right brain processing seems to not only lack precise translations into language, but gets little opportunity to do so (so, as an artist, I loved this comment from Paul Murray: "As a programmer, I have often faced the situation where right-brain-me writes some fancy code, and left-brain-me does not understand it and has to be reassured that it really will work. The reassurance is sort of a wordless "yes, I checked it and it's ok, I promise".

By Crowknows (not verified) on 06 Jul 2008 #permalink