July 13, 2021 (from www.rationaloptimist.wordpress.com)
Though some people are called brainless, most would say they have one brain. But how many minds do you have? Perhaps a trickier question. You might say you’re “of two minds” about an issue. There’s even a phenomenon called “split personality” (or “multiple personality disorder”).
While we do talk of “the brain” as a unit, we also speak of right and left brains with differing functionalities. The left brain being more logical, the right more intuitive and creative, and so forth. But there have been cases of people losing one hemisphere, yet able to live fairly normally, the remaining hemisphere taking over the other’s duties. On the other hand, I’ve written about a stroke victim whose damage was in the right hemisphere, enabling the left to become more dominant, changing her personality.*
But it gets yet more interesting.
The two hemispheres are really quite separate physically, being connected only by a clutch of fibers called the corpus callosum. A conduit for messaging between them. Now, it’s been found some epileptics can be helped by severing the corpus callosum, keeping seizures from passing between hemispheres. The patients seemingly unharmed.
They’ve been the subject of experiments testing the effects of thusly splitting the brain. Each hemisphere controls the opposite side the body. You can show each eye different things. In one experiment, the right eye saw a snow scene, the left a chicken claw. Next, the subject was asked to choose something related from among a group of various pictures. One hand picked a snow shovel; the other a chicken. Logical enough.
But then the subject was asked why he’d picked the shovel, which he could see he’d done. However, the speech center is in the right hemisphere, so it does the talking. And the right hemisphere was unaware of the left’s (through the right eye) having previously seen a snow picture. So he answered, “The shovel is to clean up the chicken shit.” In other words, having no access to the real reason, lodged in the other half of his brain, the half that answered made up something plausible.
This shows just how separate our two hemispheres can be. And the import can be greater than mere choosing among pictures. In one case, a man’s arm reached to hug his wife, while the other arm punched her! Neuroscientist V.S. Ramachandran reports a patient whose right brain professed a religious belief while the left said he’s an atheist (logically enough). One can imagine two hands fighting over an election ballot.
The real-life model for the character played by Dustin Hoffman in the film Rain Man was found to have been born without a corpus callosum. He could read two pages of a book simultaneously, one with each eye. Memorizing each too, instantly.
All this helps us regarding the problem of understanding consciousness and the self. Which in fact science has not yet cracked. The split-brain stuff reminds me of Daniel Dennett’s concept in his (optimistically titled) book Consciousness Explained. He rejected our commonplace notion of some sort of captain at the helm in our minds, the “I,” who makes decisions. Dennett said it’s more like a scrum of mates fighting over control of the wheel. And it does seem that a lot of competing and often contradictory notions bubble up out of various modules in the brain each running their own separate sequences, until one dominates sufficiently to cause an action to be performed.
Some see the split-brain experiments as showing we are all actually “split personalities.” That we really do have two separate minds co-existing within our skulls, one in each hemisphere.
But let’s remember that literal split-brain is a very special case. Most of us have an intact corpus callosum enabling the two hemispheres to coordinate. Like in a marriage, only more so. I think that normally the two hemispheres work things out. When they can’t, that’s mental illness.