Know Your Brain: How The Left and Right Hemispheres Operate

(Editor’s note: This article is from the Summer 2016 issue of Brain World magazine. If you enjoy this article, please support us with a print or digital subscription!)


In ancient Greece, left-brain creativity was attributed to the god Dionysus (the god of wine and drunkenness) while traits of reason and order were ascribed to Apollo — dualities of human nature that to this day are equally prized. The trouble is, this type of thinking is not entirely accurate. At least once in your life you’ve probably described yourself as either left- or right-brained, or probably taken one of those Facebook quizzes to help determine your disposition. Chances are if you scored higher right-brain results, you think of yourself as creative — with a knack for writing poetry or music, working better with brush strokes than math equations. Those of you who scored higher left-brain results would probably be better described as analytical, rational thinkers who aren’t too afraid to attack abstract problems.

While people have long been aware of human nature’s duality, it was only around 1861 that the legendary work of Paul Broca made the scientific world aware that the left hemisphere of the brain is responsible for speech. Broca, a French physician, identified a syphilitic lesion on the left frontal lobe of his patient “Tan.” Tan suffered from a severe condition known as expressive aphasia, which made processing speech difficult — his nickname came from one of the few words he was able to articulate. It became clear to Broca that speech processing originated from the left hemisphere of the brain.

One century later, however, the picture got a bit more complicated, when pioneer neuroscientists Michael Gazzaniga and Roger Wolcott Sperry found that their split-brain patients processed visual stimuli using the opposite hemisphere. The test subjects were given a list of everyday items to label, and while it was clear that the objects were familiar — a task of the right hemisphere — the patients could not assign them names (as language is controlled by the left hemisphere).

CROSSTALK

So what’s really going on here? The halves are actually a bit more dependent on each other than pop psychology has you believe. Thoughts occurring in one hemisphere (stimulation, such as seeing the perfect sunset for your landscape) can cause contractions in the opposite hemisphere, activating areas of memory and language — it’s also why you may not always be the best at describing your scene in words on paper. Although distinct, the hemispheres regularly communicate, doing this with excitatory and inhibitory signals that carry across the corpus callosum and elsewhere. Both the left hemisphere (LHS) and right hemisphere (RHS) offer their own ways to decrypt these signals. It’s called hemispheric rivalry — a regular discussion going on in your head as you process the situation before you and ultimately decide how to act. Do you pretend you don’t see your former roommate, or do you greet them? Consciousness could be defined by the way we make use of both parts of the brain.

What would the LHS say to do in the midst of this rivalry? It is somewhat of a risk taker, making it the driving force behind some of our more reckless decisions. Maybe you’re still angry about the time your roommate decided to move out abruptly and left you stuck with four months of your lease. The emotions from this past occurrence feed into your LHS and, if you aren’t careful, could probably push you to angrily rebuke your old roommate in public. Not every plan developed in the LHS is a dangerous one — but usually is an illogical response, not fully thought out. A mediation between the LHS and RHS could lead you to simply walk away without acknowledging your roommate. In many ways, the RHS is the inaction, or the equal opposite of LHS, making use of logic and calculations before acting.

How did the brain come equipped with this foundational mediation? In the earlier days of our evolution, risk-taking was an essential part of our survival. To not hunt or seek new grounds for shelter during extreme weather — such as the shifting climates that  encouraged human migration through Africa — would mean surrendering to the elements. The RHS had much less time to develop, according to an anthropological perspective, evolving only as things became more stable — environments where dangers from an animal attack, or a marauding tribe, were more likely than starvation, where one would want to minimize the risk of a confrontation rather than provoke one.

Although centuries have passed, these traits are still detectable in the modern world, changing with the environments where people live. Since we are social beings, affecting each other without even realizing it, people in developed areas of the world display a prevalence of RHS domination. The reverse is common in developing regions of the world and places with extreme climate. Many of the ancient tribes of the Arctic were LHS-dominant cultures. These traits are hardly unique to people, for that matter. Studies of birds like the Chickadee are consistent with these results. Chickadees indigenous to Canada have LHS dominance compared to their relatives from Texas. One experiment had the populations change places, and the action-reliant Texans soon became prevalent in the Yukon.

When saying that either the LHS or RHS becomes dominant, bear in mind that both hemispheres of the brain continue to function, but during interactions, one side gradually becomes dominant, drowning the other out. In the moment right before we act, but have already decided to do so, we are changing the state of our brains, shifting the weight balanced by each hemisphere.

Whether we act or not, we impact the way in which one hemisphere can mute out the other. At the same time, the less effective, restricted hemisphere learns how to give off more excitatory signals with more frequency for next time. If you choose to splurge on dessert, your LHS has effectively inhibited the RHS and altered the power dynamic, making the LHS just slightly more dominant than the submissive RHS. If you choose to avoid the calories, then the reverse happens.

Over one’s lifetime, these decisions in an ever-changing anatomy, along with one’s own environment, will determine both the structure and plasticity of the individual’s brain. If you happen to think of your life as dull and suburban, chances are that your LHS contains fewer distinct neural networks than the RHS. In individuals that are violent offenders, the LHS appears much more distinct and pronounced than their RHS.

However, veteran gang members have displayed some of the most visible symmetry between both hemispheres of the brain. Although these individuals show an amazing propensity to behave in extremely risky ways — the ruthlessness needed for doing business with dangerous associates, or just for surviving in high-stress environments like prison — they also prove to be just as capable of inhibiting themselves from acting out.

FOLLOWING THE SYNAPTIC TRAIL

To more fully understand the operations between the cerebral hemispheres, one must follow the path of the neural networks around them. Our association of the LHS with action and emotion is because of its connectivity to specialized parts in the brain across both hemispheres that play a role in those behaviors. Most significant are LHS connections to both the brain’s insular cortex (a key part of consciousness and self-awareness — the reason we took that Facebook quiz in the first place) and the amygdala, which is critical in decision-making and memory-manufacturing.

Our association of the RHS with inaction and calculation is because of its neural networks that attach to the anterior cingulate (likewise involved in decision-making, but also error detection and reward anticipation — allowing you to see the long-term benefits of putting off the dessert) as well as the orbitofrontal and prefrontal cortices (which signal possibilities of punishment and reward with each decision).

Describing oneself as left- or right-brained hardly seems to give an accurate portrait of ourselves at all. The plasticity of our brains is constantly at work, causing dozens of changes at every moment. Involuntarily, information is passing back and forth between the hemispheres. Even patients suffering damage to the LHS have been able to form neural connections in the RHS to carry out the tasks traditionally associated with the LHS.


Those with RHS damage show a high degree of functionality in motor skills after new neural connections develop in the LHS. Despite grievous injuries, these shifts continue to occur, even on the level of neurons, which gather on each side when signaled by the RHS. This shift in the neurons’ functioning is actually similar to what occurs in people who lose their sense of sight or hearing, and when specialized neurons serve to boost the other senses to compensate for the loss.

(Editor’s note: This article is from the Summer 2016 issue of Brain World magazine. If you enjoy this article, please support us with a print or digital subscription!)

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