Numerous functional neuroimaging studies reported increased activity in the middorsolateral prefrontal cortex (MDLFC) and the posterior parietal cortex (PPC) during the performance of working memory tasks. However, the role of the PPC in working memory is not understood and, although there is strong evidence that the MDLFC is involved in the monitoring of information in working memory, it is also often stated that it is involved in the manipulation of such information. This event-related functional magnetic resonance imaging study compared brain activity during the performance of working memory trials in which either monitoring or manipulation of information was required. The results show that the PPC is centrally involved in manipulation processes, whereas activation of the MDLFC is related to the monitoring of the information that is being manipulated. This study provides dissociation of activation in these two regions and, thus, succeeds in further specifying their relative contribution to working memory.fMRI ͉ middorsolateral prefrontal cortex ͉ intraparietal sulcus region ͉ working memory A lthough it is now clear that both the MDLFC and the PPC play an important role in working memory (1-6), the relative contribution of these two regions is not well understood. For instance, it is often stated that the MDLFC is involved in a variety of high-order cognitive processes such as the monitoring (1, 2, 7, 8) and manipulation (6, 9-11) of information in working memory, but the relation between these two processes needs clarification. Monitoring, as a functional role of the MDLFC, was defined as the process of keeping track of the current status of events in relation to other events in working memory (7, 10). Manipulation (i.e., the rearrangement) of items of information in working memory, which can operationally be defined as the reordering or transformation of these items, necessarily involves the monitoring of the information that is being manipulated in working memory (i.e., keeping track of the status of each item in relation to other items as they are being rearranged). Monitoring, however, can also be tested in working memory tasks that do not involve rearrangement of items (8,12). The suggestion that the monitoring of events in working memory is the critical contribution of the MDLFC to cognitive control was first made by Petrides (8, 12) on the basis of studies demonstrating that lesions limited to this cortical region in monkeys impair severely performance on working memory tasks that require monitoring of items without involving any manipulation of those items. For instance, monkeys with MDLFC lesions are impaired on a working memory task in which a random subset of stimuli from an expected set is presented (e.g., two visual objects from a familiar set of three), and the animals simply have to monitor the stimuli that occurred so that they can decide, on the test trial, which one of the three stimuli has not been presented (see ref.12, experiments 2 and 3). Thus, although the current standard view of the...
Studies that have investigated prism adaptation (PA) effects on symptoms of visuospatial neglect have primarily used neuropsychological tests as outcome measures. An important question that remains to be answered is whether PA effects translate into improvements in patients' daily life activities. In the present review, we examined systematically the evidence for the effect of PA treatment on daily life activities in patients with neglect. Two authors independently assessed the methodological quality of 25 intervention and 1 follow-up studies using validated scales. PA effects were evaluated for reading/writing, activities of daily living (ADL) direct tests, ADL questionnaires, and navigation tests. Studies were evaluated as being of excellent (n = 1), good (n = 12), fair (n = 10), or poor (n = 3) quality. Among the 26 articles, a total of 32 measurements showed significant PA effects (one measurement from a study of excellent quality, 17 from studies of good quality, 10 from studies of fair quality, four from studies of poor quality), whereas non-significant effects were found in 15 measurements (two from a study of excellent quality, three from studies of good quality, eight from studies of fair quality, two from studies of poor quality). There is some evidence suggesting that PA can improve daily functioning, particularly as measured by reading/writing and ADL direct tests. The impact of several variables on PA effects should be investigated further including sample heterogeneity and time since injury.
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