The Mind and the Brain by Jeffrey M. Schwartz, Sharon Begley Page A
Authors: Jeffrey M. Schwartz, Sharon Begley
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be found between striosomes and matrisomes.Striosomes are areas where information from an emotion-processing part of the brain, the amygdala, reaches the caudate; matrisomes are clumps of axon terminals where information from the thinking, reasoning cerebral cortex reaches the caudate. By virtue of their position, TANs can integrate emotion and thought.They fire in a characteristic pattern when the brain senses something with positive or negative emotional meaning. Cognitive-behavioral therapy may change how TANs respond to OCD triggers.
TANs respond dramatically to visual or auditory stimuli that are linked, through behavioral conditioning, to a reward. As a result of this finding, Graybiel’s team began to suspect that TANs play a central role in behavioral responses to hints of an upcoming reward. In a series of experiments on macaque monkeys, the MIT scientists found that TAN firing rates changed when a once-neutral cue became associated with a reward. Let’s say, for instance, that a visual cue such as a flashing light means that the monkey will get a reward (juice) if it performs a simple behavioral response (licking a spoon). When TANs detect a potential reward, that is, they pause at first and then fire faster. But TANs do not respond to the light cue if the monkey has not learned to associate it with a reward. Asthe monkey’s brain learns to recognize a reward, TANs fire in a characteristic pattern.
Thanks to its TAN cells, then, the striatum is able to associate rewarded behavior with particular cues. Because TANs can quickly signal a switch in behavioral response depending on the meaning of a stimulus (“That light means juice!”), they may serve as a sort of gating mechanism, redirecting information flow through the striatum during learning. As noted earlier, the entire striatum acts as an automatic transmission: the putamen shifts between motor activities, and the caudate nucleus shifts between thoughts and emotions. Different gating patterns in the striatum may thus play a critical role in establishing patterns of motor as well as cognitive and emotional responses to the environment. Such patterned responses are nothing more than habits. Indeed, Graybiel has shown that the striatum can play a fundamental role in the development of habits. Our best guess is that the tonically active neurons underpin the gating of information through the striatum and thus its role in the formation of habits. What seems to happen is that distinct environmental cues, associated with differing emotional meanings, elicit different behavioral and cognitive responses as TANs shift the output flow of the striatum. In this way TANs may serve as the foundation for the development of new patterns of activity in the striatum.
Most important, TANs could be crucial to the acquisition of new behavioral skills in cognitive-behavioral therapy. In neurological terms, we could say that cognitive-behavioral therapy teaches people purposefully to alter the response contingencies of their own TANs. This is a crucial point. Such therapy teaches people to alter, by force of will, the response habits wired into their brains through TANs. In the case of OCD, therapy teaches patients to reinterpret their environment and apply their will to alter what had been an automatic behavioral response to disturbing feelings. If that happens often enough, then the new response—the new behavioral output—should itself become habitual. The key to a successfulbehavioral intervention in OCD, it seemed to me, would be to teach the striatum new gating patterns.
The gating image turns out to be particularly apt in light of what we have learned about the striatum’s two output pathways: one direct and one indirect. The indirect pathway takes the scenic route, running from the striatum through the globus pallidus, to the subthalamic nucleus, back to the globus pallidus, and finally to the thalamus and cortex. The direct pathway runs through the globus pallidus,
TANs respond dramatically to visual or auditory stimuli that are linked, through behavioral conditioning, to a reward. As a result of this finding, Graybiel’s team began to suspect that TANs play a central role in behavioral responses to hints of an upcoming reward. In a series of experiments on macaque monkeys, the MIT scientists found that TAN firing rates changed when a once-neutral cue became associated with a reward. Let’s say, for instance, that a visual cue such as a flashing light means that the monkey will get a reward (juice) if it performs a simple behavioral response (licking a spoon). When TANs detect a potential reward, that is, they pause at first and then fire faster. But TANs do not respond to the light cue if the monkey has not learned to associate it with a reward. Asthe monkey’s brain learns to recognize a reward, TANs fire in a characteristic pattern.
Thanks to its TAN cells, then, the striatum is able to associate rewarded behavior with particular cues. Because TANs can quickly signal a switch in behavioral response depending on the meaning of a stimulus (“That light means juice!”), they may serve as a sort of gating mechanism, redirecting information flow through the striatum during learning. As noted earlier, the entire striatum acts as an automatic transmission: the putamen shifts between motor activities, and the caudate nucleus shifts between thoughts and emotions. Different gating patterns in the striatum may thus play a critical role in establishing patterns of motor as well as cognitive and emotional responses to the environment. Such patterned responses are nothing more than habits. Indeed, Graybiel has shown that the striatum can play a fundamental role in the development of habits. Our best guess is that the tonically active neurons underpin the gating of information through the striatum and thus its role in the formation of habits. What seems to happen is that distinct environmental cues, associated with differing emotional meanings, elicit different behavioral and cognitive responses as TANs shift the output flow of the striatum. In this way TANs may serve as the foundation for the development of new patterns of activity in the striatum.
Most important, TANs could be crucial to the acquisition of new behavioral skills in cognitive-behavioral therapy. In neurological terms, we could say that cognitive-behavioral therapy teaches people purposefully to alter the response contingencies of their own TANs. This is a crucial point. Such therapy teaches people to alter, by force of will, the response habits wired into their brains through TANs. In the case of OCD, therapy teaches patients to reinterpret their environment and apply their will to alter what had been an automatic behavioral response to disturbing feelings. If that happens often enough, then the new response—the new behavioral output—should itself become habitual. The key to a successfulbehavioral intervention in OCD, it seemed to me, would be to teach the striatum new gating patterns.
The gating image turns out to be particularly apt in light of what we have learned about the striatum’s two output pathways: one direct and one indirect. The indirect pathway takes the scenic route, running from the striatum through the globus pallidus, to the subthalamic nucleus, back to the globus pallidus, and finally to the thalamus and cortex. The direct pathway runs through the globus pallidus,
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