Hemispheres

What other features of our brains determine our social and political views and behaviors?

As it turns out, one of the most important is found between the hemispheres of the brain.

We've all heard the Left Brain, Right Brain arguments in the past - cliches from a generation ago, nurtured by pop culture, that tell us "left-brained" people are logical and verbal, while "right-brained" people are emotional and creative. Many of us have been exposed to this concept so often that we've just assumed it to be true.

The truth is far more complicated.

The expert in this area is British psychiatrist Iain McGilchrist, who has studied the actual neurophysiological divide between the left and right hemispheres of the brain through his own patients and the growing literature on the subject - in particular, those differences we see in perception, cognition, emotion and behavior when one hemisphere or the other is damaged.

He has articulated these fascinating differences in countless presentations, talks and interviews, and his own book The Master and the Emissary. He is quoted below in the Hidden Brain podcast with host Shankar Vedantam, from February 2019.

"In motor terms, it's fairly straightforward that the left hemisphere controls the right side of the body and receives messages from it and vice versa," he said. "But in terms of psychological life, they have quite different kinds of roles. They have quite different dispositions. And I believe evolutionarily, they are - if you like - addressing different questions."

Asymmetrical

First among McGilchrist's assertions is that it is an empirical certainty that the human brain's hemispheres are asymmetrical - that is, when one side is damaged, certain behaviors and deficits will emerge in the shift to dependency upon the other, and that these will differ considerably and consistently, depending on whether the damage is on the left or right.

Moreover, this asymmetry is present not only in human beings but in all mammals. For that matter, it's present in all creatures great and small - in anything that has a neural network, from reptiles to worms. And the natural question is, Why?

The answer, he said, because the old Left-Right dichotomy is wrong: the brain's two sides don't divvy up tasks into Reason Here, Emotion There; it's because the two sides of the brain do the same things differently.

The reason all creatures have a divided brain is so that they can have two different versions of reality at their disposal. Every living creature is has two tasks: 1) eat, and 2) avoid being eaten. The left hemisphere focuses on the first, the right on the second. We must have both, and they must co-exist and function simultaneously for obvious reasons: if we do one to the exclusion of the other, we either don't eat or we get eaten.

Details, details

The left hemisphere is focused on the task at hand - getting food, more often than not. It is the bird going for a worm; it is the lion pouncing on the gazelle; it is the chimp plucking a berry from a bush. The left hemisphere lives in the moment, accomplishing the job in progress.

Other examples were presented in the Hidden Brain broadcast: the left hemisphere is where the musician turns when rehearsing a trouble passage in a piano piece, practicing fingering; it is the basketball player dribbling the ball and shooting it.

The right hemisphere's task follows: for the musician, it is integrating the rehearsed passage into a full performance; it is the basketball player's awareness, while dribbling or shooting, of where all the other players are.

In the wild, while the left hemisphere is providing attention and focus on acquiring food, the right hemisphere is providing cover, maintaining global awareness of the surroundings, remembering the moments before and anticipating the moments to come.

Simplifying a not-so-simple idea, the difference boils down to this: "The right hemisphere takes in the whole at the start," McGilchrist explained. "The left hemisphere unpacks that and enriches it. But then that work being done, it needs to be taken back into the whole picture, which only the right hemisphere can do."

Both are functioning in the same place at the same time. But they are profoundly distinct: they essentially provide two different accounts of reality.

Left Meaning, Right Meaning

Nuance begins to emerge when we consider the subtleties introduced by hemispheric differences in human communication. McGilchrist points out that it's the left brain's job to perform literal interpretation; it's the right brain's job to pick up tone, implication, insinuation - not the meaning of a word, but the emotions conveyed in the way it is spoken. The left brain picks up only explicit meaning; the right brain picks up shadings in how it is conveyed.

For this reason, metaphor is particularly tricky for the left brain.

"As some philosophers have pointed out, metaphor is how we understand everything," he said. "And they point out that, actually, particularly scientific and philosophical understanding is mediated by metaphors. In other words, the only way we can understand something is in terms of something else that we think we already understand. And it's making the analogy, which is what a metaphor does, that enables us to go, 'I see, I get it.'

"Now, if you think that metaphor is just one of those dispensable decorations that you could add to meaning - it's kind of nice, but probably a distraction from the real meaning - you've got it upside down," he continued. "Because if you don't understand the metaphor, you haven't understood the meaning. Literal meaning, however, is a peripheral, diminished version of the richness of metaphorical understanding. And what we know is the right hemisphere understands those implicit meanings, those connections of meanings, what we call connotations, as well as just denotations. It understands imagery. It understands humor. It understands all of that."

Time

The left hemisphere, McGilchrist continued, is "very goal-driven, but very short-term goal-driven. It wants to grasp things that are within reach...so it has a very direct, linear idea of a target and let's go and get it."

"The left hemisphere can't deal with anything that is moving," he went on. "It fixes things. It likes things to be fixed because then you can grab them. You can't grasp your prey, you can't pick up something unless you can at least immobilize it for that second while you're interacting with it."

The right hemisphere, on the other hand, likes flow; time is a river on the right, constantly in motion.

Values

The two sides even have differing values. The immediacy and craving for the concrete, the graspable, make the left brain's concept of values very mechanical, algorithmic, while the right brain's take on values is more holistic.

"If you disable, temporarily, the right temporoparietal junction - which you can do with a painless procedure - and ask people to solve moral problems, they give quite bizarre answers to them based on an entirely utilitarian understanding of them.

"An example is, a woman is having coffee with her friend. She puts what she thinks is sugar in her friend's coffee, but it's in fact poison, and the friend dies. Scenario two, a woman is having coffee with her friend whom she hates, she wants to poison her - and she puts what she thinks is poison in the coffee, but it's sugar, and the friend lives. Which is the morally worse scenario?

"Now, all of us using our intact brains say, well, the one in which she intended to kill her friend. But no, if you disable the right hemisphere, the good old left hemisphere says, well, obviously the one in which she died. The consequence is what matters. So values are not well-appreciated, I think, by the left hemisphere."

Aware and Not

Finally, there's the question of how the two sides of the brain see each other.

Not surprisingly, as the guardian of the big picture, the right hemisphere is aware of the left, and can monitor what it is doing - that's the right hemisphere's job. The left hemisphere, on the other hand, is tasked with immediate tasks; it must maintain a narrow focus, and has no bandwidth or need for awareness of the right hemisphere. It believes that what is sees is all there is.

McGilchrist told the story of a physician and patient who had experienced right hemisphere damage. She had the odd belief that her arm did not belong to her, but that she had found it in her bed. "What we're seeing here is a phenomenon called denial, which is a feature of the way the left hemisphere works," he said. "So if you have a left hemisphere stroke, so your right hemisphere is still functioning, you're very aware of what deficits you have. If you have a right hemisphere stroke, you are completely unaware of there being anything wrong. So if you have a paralyzed left arm, which is often a consequence of a right hemisphere stroke, more often than not you will deny that there's any problem with it. If asked to move it, you will say there, but it didn't move.

"If, on the other hand, I bring it in front of you and say, 'Whose arm is this, can you move it?', they say, 'Oh, that's not mine. That belongs to you, doctor, or to the patient in the next bed'... They're simply incapable of understanding that there is something wrong here that involves them." The left brain's focus is on body parts; the right brain focuses on awareness of the body as a whole.

Emotional divide

Another difference between brain hemispheres is how emotions lateralize between them.

The big-picture orientation of the right brain makes it the center of understanding of other peoples' emotions, as they are part of that big picture. "Broadly speaking," per McGilchrist, "the right hemisphere is more emotionally literate." It is where understanding of the point of view of others emerges, and likewise enables a greater range of expression. When opposition presents itself, the impulse of the right brain is to understand and cooperate, which serves the big picture.

The intense in-the-moment focus of the left brain, on the other hand, renders it dismissive of external emotions, and self-defensively prone to anger when interrupted, which understandably serves its purpose. When opposition presents itself, the impulse of the left brain is to obstruct and repel, which serves the success of the immediate task.

We are left with a complicated but compelling portrait of how our brains move us through the world and through our lives, once McGilchrist's portrait of the hemispheres has been thoroughly reviewed. It's easy to see how the pieces fit together, how their cooperation has kept us alive and thriving and - perhaps most importantly - that we can't manage without both.