A Saturday Essay in the Wall Street Journal this weekend explained why theories about hemisphere dominance in the brain are outdated and outlined a "new" brain function map that is much more nuanced.
The origins of the left-brain, right-brain theory dates back to experimental surgeries performed on 16 patients with severe epilepsy about 50 years ago, write neuroscientist Stephen Kosslyn and author Wayne Miller.
In those surgeries, Roger Sperry—a renowned neuroscientist at the California Institute of Technology—sought to relieve the patients' suffering by severing their corpus callosum, a bundle of nerve fibers that connects the two sides of the brain.
The surgeries were successful, and post-operative studies of the volunteers found that the two brain halves do have distinct capabilities. However, contrary to popular narrative, the difference in capabilities reflect very specific differences in function, such as paying attention to overall shape versus details during perception. However, this "fine print" got buried in the publicity generated by Sperry's research.
To better understand brain function, we should focus on the anatomical division between the top and bottom halves, write Kosslyn and Miller. This approach—called the theory of cognitive modes—came from a landmark study published in 1982 by the National Institutes of Mental Health's Mortimer Mishkin and Leslie G. Ungerleider. Subsequent studies have reinforced the approach.
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The theory holds that the top-brain system, which is composed of the entire parietal lobe and the top portion of the frontal lobe, uses information about the surrounding environment in combination with emotional reactions and personal needs to decide which goals to try and achieve. The top-brain formulates plans, generates expectations about what will happen when the plan is executed, and—as the plan is being carried out—makes adjustments.
Meanwhile, the bottom-brain system, which is composed of the occipital and temporal lobes and the smaller remainder of the frontal lobe, organizes sensory signals, simultaneously comparing what is being perceived with information stored in memory. The bottom-brain uses the information from the comparisons to classify and interpret an object or event, drawing meaning from the world.
Kosslyn and Miller stress that the top- and bottom-brain systems work together and are not engaged in a "constant cerebral tug of war."
However, individuals do not rely on the top and bottom parts of their brains equally. Rather, some use the top-brain system to develop simple and straightforward plans, while others use the bottom-brain system to create more detailed plans based on the subtleties of a given situation.
The new cognitive theory offers a new way of looking at human thought and behavior that could help explain our actions and personalities. It predicts that individuals fit into one of four cognitive modes based on their reliance on the top and bottom brain:
It is important to note that no one mode is "better" than the others, Kosslyn and Miller stress. Rather, the theory reinforces the notion that people can work together more productively when they are aware of their own and others' cognitive strengths and weaknesses (Kosslyn/Miller, Wall Street Journal, 10/18).
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