Know Your Brain: How The Left and Right Hemispheres Operate


brain hemispheres

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).


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.

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