It's a Jungle in There: How Competition and Cooperation in the Brain Shape the Mind by David A. Rosenbaum Page A
Authors: David A. Rosenbaum
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hemisphere could not. Meanwhile, the left hemisphere could display verbal recognition of the seen object, but the right hemisphere could not.
These results and others led Gazzaniga and Sperry to propose that different “mega-functions” are served by the left and right cerebral hemispheres. The left cerebral hemisphere supports verbal-analytic thinking, while the right cerebral hemisphere supports nonverbal-holistic thinking. In terms of the broader message of this chapter, just as macroscopic differences can be found between ecosystems in the outer world, macroscopic functional differences can be found between neural systems in the brain.
Methods for Identifying Brain Specialization
At this point, I could ask you to join me on a more detailed tour of the brain, considering what the many parts of the brain do—what functions, in other words, those brain regions seem to carry out with regard to cognition, perception, action, and emotion. We could move from place to place, noting the apparent specialization of each locale. The review would show that things change gradually as we move from one neural neighborhood to the next.
I will refrain from providing such a tour, however, because we could lose sight of the larger principle I want to emphasize. It suffices to say, in my opinion, that there are three aspects of brain specialization that bear on the jungle principle. These pertain to the methods used to infer the specialization, the claim that brain functions are localized, and the issue of whether the brain is hard- or soft-wired. 11 I’ll take up each of these issues in this and the next two sections.
Regarding method, it pays to consider how the functional properties of different brain regions are discerned. One method—perhaps the most straightforward—is to ask what happens when a part of the brain is damaged. The logic is straightforward. If damage to some brain region disrupts some activity, then that region can be said to play some role in that activity.
Sometimes people go beyond this modest inference and say that if damage to a part of the brain impairs an activity, then that part of the brain
controls
that activity or is
necessary
for that activity. Such a conclusion is premature, however, and here’s an anecdote that shows why.
Suppose you’re a songwriter and, like many aspiring tune-and-lyric creators, you write songs at home. One day, something annoying happens. The sewer line running from your house backs up and your basement starts to fill with the most foul-smelling ooze. I think of this disgusting example because this happened at my house one day while I was writing this book. I couldn’t get the experience out of my mind and thought of it as I started to write this section.
If your sewer line backs up while you’re trying to compose music, your writing suffers. In fact, your composing comes to a screeching halt, not because your sewer line is strictly necessary for your music generation, but because the unexpected plumbing problem interferes with your ability to concentrate on your art. This homely example shows how careful one must be about drawing causal conclusions from neural damage. If neural damage disrupts an activity, it doesn’t follow that the activity depends in a direct way on the region that’s impaired.
Now consider another possible outcome—that damage to some area of the brain does
not
impair or affect a function. What can you conclude from that outcome? You have to be careful here as well. You’d be incorrect to say that the lack of an effect following damage to that brain area implies that the brain area plays no role in the function. The brain area
might
play a role, but there might also be a backup system that takes over if the area takes a hit.
These cautions aside, it’s unquestionable that a vast amount has been learned about the brain and nervous system by studying the effects of damage to its components. Such damage can result from accidents such as bullet
These results and others led Gazzaniga and Sperry to propose that different “mega-functions” are served by the left and right cerebral hemispheres. The left cerebral hemisphere supports verbal-analytic thinking, while the right cerebral hemisphere supports nonverbal-holistic thinking. In terms of the broader message of this chapter, just as macroscopic differences can be found between ecosystems in the outer world, macroscopic functional differences can be found between neural systems in the brain.
Methods for Identifying Brain Specialization
At this point, I could ask you to join me on a more detailed tour of the brain, considering what the many parts of the brain do—what functions, in other words, those brain regions seem to carry out with regard to cognition, perception, action, and emotion. We could move from place to place, noting the apparent specialization of each locale. The review would show that things change gradually as we move from one neural neighborhood to the next.
I will refrain from providing such a tour, however, because we could lose sight of the larger principle I want to emphasize. It suffices to say, in my opinion, that there are three aspects of brain specialization that bear on the jungle principle. These pertain to the methods used to infer the specialization, the claim that brain functions are localized, and the issue of whether the brain is hard- or soft-wired. 11 I’ll take up each of these issues in this and the next two sections.
Regarding method, it pays to consider how the functional properties of different brain regions are discerned. One method—perhaps the most straightforward—is to ask what happens when a part of the brain is damaged. The logic is straightforward. If damage to some brain region disrupts some activity, then that region can be said to play some role in that activity.
Sometimes people go beyond this modest inference and say that if damage to a part of the brain impairs an activity, then that part of the brain
controls
that activity or is
necessary
for that activity. Such a conclusion is premature, however, and here’s an anecdote that shows why.
Suppose you’re a songwriter and, like many aspiring tune-and-lyric creators, you write songs at home. One day, something annoying happens. The sewer line running from your house backs up and your basement starts to fill with the most foul-smelling ooze. I think of this disgusting example because this happened at my house one day while I was writing this book. I couldn’t get the experience out of my mind and thought of it as I started to write this section.
If your sewer line backs up while you’re trying to compose music, your writing suffers. In fact, your composing comes to a screeching halt, not because your sewer line is strictly necessary for your music generation, but because the unexpected plumbing problem interferes with your ability to concentrate on your art. This homely example shows how careful one must be about drawing causal conclusions from neural damage. If neural damage disrupts an activity, it doesn’t follow that the activity depends in a direct way on the region that’s impaired.
Now consider another possible outcome—that damage to some area of the brain does
not
impair or affect a function. What can you conclude from that outcome? You have to be careful here as well. You’d be incorrect to say that the lack of an effect following damage to that brain area implies that the brain area plays no role in the function. The brain area
might
play a role, but there might also be a backup system that takes over if the area takes a hit.
These cautions aside, it’s unquestionable that a vast amount has been learned about the brain and nervous system by studying the effects of damage to its components. Such damage can result from accidents such as bullet
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