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Prefrontal cortex
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The prefrontal cortex is the anterior part of the frontal lobes of the brain, lying in front of the motor and premotor areas. In terms of its cytoarchitectonics, the prefrontal cortex is defined by the presence of an internal granular layer IV (in contrast to the agranular premotor cortex). The prefrontal cortex can be divided in several ways, one of which is into three basic areas:
Other areas that can be distinguished are the ventrolateral cortex (vl-PFC), the medial prefrontal cortex (m-PFC), and the anterior prefrontal cortex (a-PFC).
This brain region has been implicated in planning complex cognitive behaviors, personality expression, decision making and moderating correct social behavior.
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Encyclopedia
The prefrontal cortex is the anterior part of the frontal lobes of the brain, lying in front of the motor and premotor areas. In terms of its cytoarchitectonics, the prefrontal cortex is defined by the presence of an internal granular layer IV (in contrast to the agranular premotor cortex). The prefrontal cortex can be divided in several ways, one of which is into three basic areas:
Other areas that can be distinguished are the ventrolateral cortex (vl-PFC), the medial prefrontal cortex (m-PFC), and the anterior prefrontal cortex (a-PFC).
This brain region has been implicated in planning complex cognitive behaviors, personality expression, decision making and moderating correct social behavior. The basic activity of this brain region is considered to be orchestration of thoughts and actions in accordance with internal goals.
The most typical psychological term for functions carried out by the pre-frontal cortex area is executive function. Executive function relates to abilities to differentiate among conflicting thoughts, determine good and bad, better and best, same and different, future consequences of current activities, working toward a defined goal, prediction of outcomes, expectation based on actions, and social "control" (the ability to suppress urges that, if not suppressed, could lead to socially-unacceptable outcomes).
Many authors have indicated an integral link between a person's personality and the functions of the prefrontal cortex.
Interconnections
The prefrontal cortex has a high number of interconnections between both the brainstem's Reticular Activating System (RAS) and the limbic system. As a result, the centers in the prefrontal cortex depend significantly on high levels of alertness, and emotional linkages with deeper brain structures related to control of pleasure, pain, anger, rage, panic, aggression (fight-flight-freeze responses), and basic sexual responses.
Studies
Perhaps the seminal case in prefrontal cortex function is that of Phineas Gage, whose personality may have changed after an 1848 accident destroyed one or both frontal lobes. The standard presentation (e.g. ) is that although Gage retained normal memory, speech and motor skills, his personality changed radically. He became irritable, quick-tempered, and impatient, characteristics that he previously did not exhibit, so that friends described him as "no longer Gage." And whereas he had previously been a capable and efficient worker, afterwards he was unable to complete the multiple tasks that he started. However, careful analysis of primary evidence shows that descriptions of Gage's psychological changes are usually exaggerated, the most striking feature being that changes described years after his death are far more dramatic than anything reported while he was alive .
Subsequent studies, on patients with prefrontal injuries, have shown that the patients verbalized what the most appropriate social responses would be under certain circumstances, yet, when actually performing, they instead pursued behavior that is aimed at immediate gratification despite knowing the longer-term results would be self-defeating.
The interpretation of this data indicates that not only are skills of comparison and understanding of eventual outcomes harbored in the prefrontal cortex but the prefrontal cortex (when functioning correctly) controls the mental option to delay immediate gratification for a better or more rewarding longer-term gratification result. This ability to wait for a reward is one of the key pieces that define optimal executive function of the human brain.
There is much current research devoted to understanding the role of the prefrontal cortex in neurological disorders. Many diseases, such as schizophrenia, bipolar disorder and ADHD, have been related to dysfunction of the prefrontal cortex, and thus this area of the brain offers the potential for new treatments of these diseases. Clinical trials have begun around certain drugs that have been shown to improve prefrontal cortex function, including guanfacine which acts through the alpha-2A adrenergic receptor. A downstream target of this drug, the HCN channel, is one of the most recent areas of exploration in prefrontal cortex pharmacology.
Miller and Cohen propose an Integrative Theory of Prefrontal Cortex Function. The two theorize that “cognitive control stems from the active maintenance of patterns of activity in the prefrontal cortex that represents goals and means to achieve them. They provide bias signals to other brain structures whose net effect is to guide the flow of activity along neural pathways that establish the proper mappings between inputs, internal states, and outputs needed to perform a given task” (Miller & Cohen, 2001). Essentially the two theorize that the prefrontal cortex guides the inputs and connections which allows for cognitive control of our actions.
The prefrontal cortex (PFC) is of significant importance when top-down processing is needed. Top-down processing by definition is when behavior is guided by internal states or intentions. According to the two, “The PFC is critical in situations when the mappings between sensory inputs, thoughts, and actions either are weakly established relative to other existing ones or are rapidly changing”(Miller & Cohen, 2001). An example of this can be portrayed in the Wisconsin card sort task (WCST). Subjects engaging in this task are instructed to sort cards according to the shape, color, or number of symbols appearing on them. The thought is that any given card can be associated with a number of actions and no single stimulus-response mapping will work. Human subjects with PFC damage are able to sort the card in the initial simple tasks, but unable to do so as the rules of classification change.
Miller and Cohen conclude that the implications of their theory can explain how much of a role the PFC has in guiding control of cognitive actions. In the researchers own words they claim that “depending on their target of influence, representations in the PFC can function variously as attentional templates, rules, or goals by providing top-down bias signals to other parts of the brain that guide the flow of activity along the pathways needed to perform a task” (Miller & Cohen, 2001).
Other disorders
In the last few decades, brain imaging systems have been used to determine brain region volumes and nerve linkages. Several studies have indicated that reduced volume and interconnections of the frontal lobes with other brain regions is observed in those with schizophrenia, depression, people subjected to repeated stressors, suicide victims, incarcerated criminals, sociopaths, and drug addicts. It is believed that at least some of the human abilities to feel guilt or remorse, and to interpret reality, lie in the prefrontal cortex. It is also widely believed that the size and number of connections in the prefrontal cortex relates directly to sentience, as the prefrontal cortex in humans occupies a far larger percentage of the brain than any other animal: as the brain has tripled in size over 5 million years of human evolution, the prefrontal cortex had increased in size sixfold.
See also
External links
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