The Mind and the Brain by Jeffrey M. Schwartz, Sharon Begley
Authors: Jeffrey M. Schwartz, Sharon Begley
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that something was. The normal subjects in the gambling study felt something was wrong when it was wrong, even if they didn’t know why. This all constitutes powerful evidence that the orbital frontal cortex is involved in generating the intuitive feeling “Something is wrong here.”
A second overactive region we detected on the PET scans of the brains of OCD patients was the striatum . This structure is composed of two major information-receiving structures, the caudate nucleus and the putamen , which nestle beside each other deep in the core of the brain just in front of the ears. The entire striatum acts as a sort of automatic transmission: the putamen acts as the gear shift for motor activity, and the caudate nucleus serves a similar function for thought and emotion. The striatum as a whole receives neuronal inputs from so many other regions of the brain that it rivals, for sheer complexity, the central switching station for the busiest telecom center imaginable, with signals arriving and departing in a buzz of perpetual activity. All areas of the cortex send neural projections to the striatum; so do parts of the thalamus and the brainstem, as shown in Figure 2 on Chapter 2.
But what particularly intrigued me was the fascinating traffic pattern connecting the striatum and the cortex. One set of neuronal projections into the striatum originates in the prefrontal cortex, especially in regions associated with planning and executing such complex behaviors as the manipulation of mental images. Small clusters of projections formed by these prefrontal arrivals are called matrisomes . The matrisomes are typically found near distinct microscopic patches that stipple the striatum; they are called striosomes . The striosomes, too, receive some input from the prefrontal cortex, in particular the areas most intimately associated with emotional expression: the orbital frontal cortex and anterior cingulate cortex. These are the very cortical structures that PET scans have shown to be overactive in OCD. But the primary inputs to these striosomes are the polar opposites of the thoughtful, rational prefrontal cortex: the striosomes are also bombarded with messages from the limbic system. The limbic system comprises the structures that play a critical role in the brain’s emotional responses, particularly fear and dread. It is the limbic system’s core structure, the amygdala, that seems to generate fear and dread. And it is the amygdala that projects most robustly into the striosomes’ distinctive patches.
The striatum, and especially the caudate, can thus be thought of as a neuronal mosaic of reason and passion. It sits smack dab at the confluence of messages bearing cognitive content (courtesy of the matrisomes, where inputs arrive from the rational prefrontal cortex) and messages shot through with emotion (thanks to the striosomes, landing zones for inputs from the limbic system). The juxtaposition of striosomes and matrisomes therefore seems highly conducive to interactions between emotion and thought. Since the striosomes receive projections primarily from the emotional centers of the limbic system and the matrisomes receive projections from the higher cognitive centers of the prefrontal cortex, together they provide the perfect mechanism of integrating the messages of the heart with those of the mind.
In the mid-1990s researchers discovered a subset of highly specialized nerve cells that provide a key to understanding how the brain integrates reason and emotion. Called tonically active neurons (TANs), these cells often sit where striosomes and matrisomes meet, as Ann Graybiel and her colleagues at the Massachusetts Institute of Technology discovered. The TANs are thus perfectlypositioned to integrate information from both structures and, by implication, from the intensely passionate limbic system and the eminently reasonable prefrontal cortex.
Figure 2: Cells in the caudate known as tonically active neurons (TANs) tend to
A second overactive region we detected on the PET scans of the brains of OCD patients was the striatum . This structure is composed of two major information-receiving structures, the caudate nucleus and the putamen , which nestle beside each other deep in the core of the brain just in front of the ears. The entire striatum acts as a sort of automatic transmission: the putamen acts as the gear shift for motor activity, and the caudate nucleus serves a similar function for thought and emotion. The striatum as a whole receives neuronal inputs from so many other regions of the brain that it rivals, for sheer complexity, the central switching station for the busiest telecom center imaginable, with signals arriving and departing in a buzz of perpetual activity. All areas of the cortex send neural projections to the striatum; so do parts of the thalamus and the brainstem, as shown in Figure 2 on Chapter 2.
But what particularly intrigued me was the fascinating traffic pattern connecting the striatum and the cortex. One set of neuronal projections into the striatum originates in the prefrontal cortex, especially in regions associated with planning and executing such complex behaviors as the manipulation of mental images. Small clusters of projections formed by these prefrontal arrivals are called matrisomes . The matrisomes are typically found near distinct microscopic patches that stipple the striatum; they are called striosomes . The striosomes, too, receive some input from the prefrontal cortex, in particular the areas most intimately associated with emotional expression: the orbital frontal cortex and anterior cingulate cortex. These are the very cortical structures that PET scans have shown to be overactive in OCD. But the primary inputs to these striosomes are the polar opposites of the thoughtful, rational prefrontal cortex: the striosomes are also bombarded with messages from the limbic system. The limbic system comprises the structures that play a critical role in the brain’s emotional responses, particularly fear and dread. It is the limbic system’s core structure, the amygdala, that seems to generate fear and dread. And it is the amygdala that projects most robustly into the striosomes’ distinctive patches.
The striatum, and especially the caudate, can thus be thought of as a neuronal mosaic of reason and passion. It sits smack dab at the confluence of messages bearing cognitive content (courtesy of the matrisomes, where inputs arrive from the rational prefrontal cortex) and messages shot through with emotion (thanks to the striosomes, landing zones for inputs from the limbic system). The juxtaposition of striosomes and matrisomes therefore seems highly conducive to interactions between emotion and thought. Since the striosomes receive projections primarily from the emotional centers of the limbic system and the matrisomes receive projections from the higher cognitive centers of the prefrontal cortex, together they provide the perfect mechanism of integrating the messages of the heart with those of the mind.
In the mid-1990s researchers discovered a subset of highly specialized nerve cells that provide a key to understanding how the brain integrates reason and emotion. Called tonically active neurons (TANs), these cells often sit where striosomes and matrisomes meet, as Ann Graybiel and her colleagues at the Massachusetts Institute of Technology discovered. The TANs are thus perfectlypositioned to integrate information from both structures and, by implication, from the intensely passionate limbic system and the eminently reasonable prefrontal cortex.
Figure 2: Cells in the caudate known as tonically active neurons (TANs) tend to
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