It's a Jungle in There: How Competition and Cooperation in the Brain Shape the Mind by David A. Rosenbaum Page B
Authors: David A. Rosenbaum
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wounds, interruptions to blood flow, or physiological mayhem wrought by cancer or infection. Interruptions of brain activity can also come about by deactivating parts of the brain through temporary (reversible) freezing, a technique used in many laboratories. 12
Other methods also exist for inferring the role of brain systems in psychological functions. These fall into two broad classes:
stimulation
and
recording
. Neurophysiologists stimulate the brain and other parts of the nervous system with electrodes and then observe the consequences of the stimulation. When stimulation of a brain site gives rise to some effect, it’s possible to infer that the brain region plays some role in the observed function. Saying that the region is
necessary
for the function is too large a leap, however, as already indicated.
It’s also possible to
record
from the brain. Doing so can be achieved with tiny electrodes that pick up the electrical activity of individual neurons orsmall sets of neurons. Alternatively, it’s possible to record from the brain as a whole or section by section, picking up larger swaths of activity. Within this class of recording methods, there are technologically advanced techniques known by an alphabet-soup’s worth of acronyms: EEG, MEG, ERP, PET, CAT, MRI, fMRI, DOI. I won’t review the methods here; doing so would take us far afield. 13 Suffice it to say that the methods have supported the view that different parts of the brain serve different functions, a principle known as localization.
Localization
One of the most famous sources of evidence for localization of function in the brain is the discovery of feature detectors in the visual cortex. These neurons were found by David Hubel and Torsten Wiesel in the early 1960s. 14 While recording from cells in this region of the cat’s brain, Hubel and Wiesel noticed that when particular visual stimuli were shown, particular cells fired. For example, a given cell emitted a burst of action potentials when a dark bar was shown. The cell fired most when the bar was oriented at 90 degrees, but the more the bar’s orientation shifted from 90 (or 270) degrees, the less vigorously the cell fired. Another cell fired the most when the same dark bar was oriented at 45 (or 135) degrees. Again, the more the bar’s orientation departed from that angle, the less vigorously the cell fired. Similar distinctions applied to other cells. The stimuli that had these effects were of various kinds. They could be bars moving along paths with particular orientations, blobs in different parts of space, and so on.
Hubel and Wiesel referred to these neurons as
feature detectors
. The two scientists also distinguished between detectors that differed with respect to the complexity of the stimuli to which the detectors responded. “Simple” cells responded to elementary feature combinations. “Complex” cells responded to more complicated feature combinations. “Hyper-complex” cells responded to still more complicated feature combinations.
Analogous cells for other sensory modalities were found as well. Other researchers found neurons that respond preferentially to sounds of different frequencies, to odors of different chemical compositions, to touches on different parts of the body, to an animal’s being in different spatial locations (so-called “place cells”), and so on. 15
Do these results imply that psychological functions are localized in the brain? The answer is no, and the reason is that detecting an aspect of a stimulus isn’t the same as experiencing it in all its aspects. In addition and no lessimportantly, none of the neurons lives alone. Each does what it does by virtue of where it lives—that is, by virtue of the other neurons with which it communicates most directly. Finally, there are limits on how far one can go with the feature detector concept. If you have detectors for faces, for example, you may or may not have a detector for your grandmother’s face.
The
Other methods also exist for inferring the role of brain systems in psychological functions. These fall into two broad classes:
stimulation
and
recording
. Neurophysiologists stimulate the brain and other parts of the nervous system with electrodes and then observe the consequences of the stimulation. When stimulation of a brain site gives rise to some effect, it’s possible to infer that the brain region plays some role in the observed function. Saying that the region is
necessary
for the function is too large a leap, however, as already indicated.
It’s also possible to
record
from the brain. Doing so can be achieved with tiny electrodes that pick up the electrical activity of individual neurons orsmall sets of neurons. Alternatively, it’s possible to record from the brain as a whole or section by section, picking up larger swaths of activity. Within this class of recording methods, there are technologically advanced techniques known by an alphabet-soup’s worth of acronyms: EEG, MEG, ERP, PET, CAT, MRI, fMRI, DOI. I won’t review the methods here; doing so would take us far afield. 13 Suffice it to say that the methods have supported the view that different parts of the brain serve different functions, a principle known as localization.
Localization
One of the most famous sources of evidence for localization of function in the brain is the discovery of feature detectors in the visual cortex. These neurons were found by David Hubel and Torsten Wiesel in the early 1960s. 14 While recording from cells in this region of the cat’s brain, Hubel and Wiesel noticed that when particular visual stimuli were shown, particular cells fired. For example, a given cell emitted a burst of action potentials when a dark bar was shown. The cell fired most when the bar was oriented at 90 degrees, but the more the bar’s orientation shifted from 90 (or 270) degrees, the less vigorously the cell fired. Another cell fired the most when the same dark bar was oriented at 45 (or 135) degrees. Again, the more the bar’s orientation departed from that angle, the less vigorously the cell fired. Similar distinctions applied to other cells. The stimuli that had these effects were of various kinds. They could be bars moving along paths with particular orientations, blobs in different parts of space, and so on.
Hubel and Wiesel referred to these neurons as
feature detectors
. The two scientists also distinguished between detectors that differed with respect to the complexity of the stimuli to which the detectors responded. “Simple” cells responded to elementary feature combinations. “Complex” cells responded to more complicated feature combinations. “Hyper-complex” cells responded to still more complicated feature combinations.
Analogous cells for other sensory modalities were found as well. Other researchers found neurons that respond preferentially to sounds of different frequencies, to odors of different chemical compositions, to touches on different parts of the body, to an animal’s being in different spatial locations (so-called “place cells”), and so on. 15
Do these results imply that psychological functions are localized in the brain? The answer is no, and the reason is that detecting an aspect of a stimulus isn’t the same as experiencing it in all its aspects. In addition and no lessimportantly, none of the neurons lives alone. Each does what it does by virtue of where it lives—that is, by virtue of the other neurons with which it communicates most directly. Finally, there are limits on how far one can go with the feature detector concept. If you have detectors for faces, for example, you may or may not have a detector for your grandmother’s face.
The
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