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Functional Fractionation of Frontal Lobe

The prefrontal cortex (PFC) is thought to play a central role in higher order ‘executive’ functions important in everyday life, such as planning, problem-solving and decision making. Disturbances in such abilities are seen after frontal lobe damage as well as in a variety of conditions, ranging from drug addiction to Parkinson’s disease, and can have a significant impact on the patient’s autonomy and quality of life. Despite its broad clinical importance, the component processes underlying complex executive functions and their neural substrates within the PFC are poorly understood. Recent advances in cognitive neuroscience provide the opportunity to develop a much more detailed understanding of the component processes of executive function, and to relate these processes to particular sub-areas within the frontal lobes. This work examined the neural substrates of frontal-executive function in human participants with focal brain damage, in order to test the hypothesis that specific cognitive processes would be affected by damage to specific sub-areas within PFC. We administered a computerized test battery consisting tasks isolating specific cognitive processes to a large group of patients with lesions affecting various sectors of the frontal lobes. Individual findings from different tasks in the test battery identified several specific structure-function relationships. These include novel findings regarding distinct roles of left lateral and dorsomedial PFC in n-back task performance, a role for ventromedial PFC in flexible stimulus-reinforcement learning, and separable contributions of left lateral and ventromedial PFC to facial emotion recognition. In addition to the findings from individual tasks, this work also identified shared and dissociable PFC contributions to performance of three classic tests of executive function hpothesized to measure distinct component processes. These findings validate behavioral measures of region-specific component processes that will be applicable to other conditions marked by executive dysfunction. This work provides converging evidence for component process accounts of executive function, and contributes to our understanding of human frontal lobe function in both health and disease.

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