A Tale of Two Brains, Coherent and Unified

In the early part of my career I studied patients who had their two brains disconnected. So the left brain was disconnected from the right. There is a big nerve track that connects them in you and me and that was sectioned by neurosurgeons in order to prevent the spread of epilepsy.

What we were responsible for was working out the functions of each hemisphere. With the two hemispheres connected you could work with them independent of the other influencing it.  So we got to study it alone and over many, many years the basic finding was that one brain didn’t know what the other one was doing. And moreover, each hemisphere has a set of specializations.

We suspected, and it turned out to be true, that the left hemisphere is the language and speech hemisphere.  The right hemisphere is good at other things, managing attention maybe and it is definitely superior in some kinds of perceptual judgments. 

I think the larger finding became evident about 20 years ago when we found out that in the left brain there is a special system that seems to always want to explain actions and moods that we have after they have occurred. So we set up experiments in which we put a question to the right non-speaking hemisphere and it in effect would direct the left hand to do something. And so the patient would do that and then we would simply say to the patient, “Well why did you do that?”  

And in that simple question came flooding out the answer that the patient would make up a story that would explain why their hand had done one thing and why the other hand had done another thing and wove a tale that made coherent as it were the behaviors that are coming from all these separate brain areas.

So the larger picture is that we have a modularized brain of thousands—who knows how many—systems that are controlling our behavior at all times.  The behavior comes out and then there is this little narrator up there that turns it into a story that makes us feel coherent and unified like we all sitting here feeling coherent and unified.  It turns out it’s a thing in the left hemisphere that does this and we called it “the interpreter” and it’s a very powerful force in the human condition and it’s always trying to figure out and seek explanations for our behavior. That is what it does.