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Cing

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DLS DMS Striatum

Prefrontal cortex

DLS DMS Striatum

Figure 32.6 Schematic showing the prefrontal cortex and striatum in human (top) and rat brain. In both instances, these regions are shades in dark gray and labeled respectively. The bottom sections show coronal sections through rat brain in which medial prefrontal cortex (MFC), cingulate cortex (Cing), and dorsolateral and dorsomedial striatum (DLS and DMS, respectively) are highlighted in dark gray. Although there is behavioral and molecular evidence to suggest the diagrammed circuitry is critical for executive function in rodents, clarification of the precise functional system in rats that supports cognition associated with ''executive function'' in humans is the subject of ongoing experiments.

terminate throughout the striatum (McGeorge and Faull, 1989). Subregions of the striatum have been shown to have different functions in learning and memory. In particular, the dorsomedial striatum (DMS) has been implicated as a necessary structure to enable behavioral flexibility (Ragozzino et al., 2002). The anterior cingulate cortex, highlighted in the coronal section of the rat brain, receives afferents from the subiculum (Finch et al., 1984) and subsequently sends efferents to the striatum (Wang and Pickel, 2000).

The prefrontal cortex mediates executive function, cognitive processes particularly vulnerable to the effects of aging. Executive function is complex; it can be defined as choosing and implementing a strategy to achieve goal-directed behavior, coordinating the execution of the strategy, and disabling it afterwards (Band et al., 2002). This combination of factors enables one to effectively alter one's behavior in response to changing environmental contingencies. Hence, executive function can be evaluated using tasks designed to assess a subject's ability to inhibit a previously learned rule in order to replace it with a new, more effective rule. Attentional set shifting is such a task. Set shifting is the ability to shift attention (attentional "set") from one perceptual feature of a stimulus (e.g., shape) to another, previously irrelevant and disregarded feature of a stimulus (e.g., color). The Wisconsin Card Sort Test (WCST) is often used to evaluate set shifting in humans. During the shift phase of the WCST, Positron Emission Tomography (PET) imaging has demonstrated an increase in activity of the prefrontal cortex (Nagahama et al., 1997). Older adults display more perseverative behavior in the WCST and also show reduced prefrontal activation in response to task demands (Ridderinkhof et al., 2002; Nagahama et al., 1997). In a similar test, aged Rhesus monkeys were also impaired in set shifting, reflected by an increase in perseverative errors (Moore et al., 2003).

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Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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