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| Michael Petrides |
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McGill Univ., Montreal Neurol. Inst., Montreal, Canada
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Presentation: |
| 2002-10-10, 15:00-15:30 |
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| Frontal cortex. |
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| Although it is generally agreed that the lateral prefrontal cortex plays an important role in memory, a precise characterization of the role of the different prefrontal regions in memory has proven elusive. Earlier studies on nonhuman primates had shown that lesions of the mid-portion of the dorsolateral prefrontal cortex (areas 46 and 9/46) give rise to severe impairments on spatial and nonspatial working memory tasks that require monitoring of information in working memory. Consistent with these findings from lesion studies, functional neuroimaging work on normal human subjects has shown specific increases of activity in the human mid-dorsolateral prefrontal cortex in relation to the need to track events in working memory. In more recent experiments, we have examined the role of the mid-ventrolateral prefrontal region (areas 45 and 47/12) in memory. This work indicates that the mid-ventrolateral prefrontal cortex is selectively involved in the active retrieval of information from posterior cortical association areas. Active retrieval is required when stimuli in memory do not bear stable relations to each other and therefore retrieval cannot be automatically driven by strong, stable and unambiguous stimulus or context relations. Data from functional activation studies with normal human subjects will be presented that show specific changes in activity within the mid-ventrolateral region of the frontal cortex in relation to the active retrieval of information from memory. No changes in activity in the mid-dorsolateral region of the frontal cortex are observed when the requirement for monitoring of information is minimized. Finally, if the subject is actively attempting to encode information in a situation where monitoring requirements are minimized, specific activity increases within the orbitofrontal cortex can be demonstrated and these specific activity changes co-occur with similar activity within the limbic medial temporal region. These results are consistent with the known massive and preferential anatomical connections that the orbitofrontal cortex maintains with the medial temporal region. |
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