آیا قشر جداری جانبی از حافظه اپیزودیک پشتیبانی می کند؟ مدارک و شواهد از بیماران ضایعه کانونی
|کد مقاله||سال انتشار||مقاله انگلیسی||ترجمه فارسی||تعداد کلمات|
|33625||2008||23 صفحه PDF||سفارش دهید||11119 کلمه|
Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Neuropsychologia, Volume 46, Issue 7, June 2008, Pages 1743–1755
Although neuroimaging and human lesion studies agree that the medial parietal region plays a critical role in episodic memory, many neuroimaging studies have also implicated lateral parietal cortex, leading some researchers to suggest that the lateral region plays a heretofore underappreciated role in episodic memory. Because there are very few extant lesion data on this matter, we examined memory in six cases of focal lateral parietal damage, using both clinical and experimental measures, in which we distinguished between recollection and familiarity. The patients did not have amnesia, but they did show evidence of disrupted recollection on an anterograde memory task. Although the exact mechanisms remain to be elucidated, lateral parietal damage appears to impair some aspects of episodic memory.
Medial temporal and prefrontal regions of the brain are necessary for episodic memory (i.e., conscious memory for personally experienced events within a particular spatiotemporal context; for reviews, see Baldo & Shimamura, 2002; Davidson, Troyer, & Moscovitch, 2006; Moscovitch, Nadel, Winocur, Gilboa, & Rosenbaum, 2006; Moscovitch et al., 2005; Squire, Stark, & Clark, 2004; Tulving, 2002). Recently, however, several independent reviews (Naghavi & Nyberg, 2005; Skinner & Fernandes, 2007; Wagner, Shannon, Kahn, & Buckner, 2005), following Rugg and colleagues’ observations with event-related potentials (e.g., Rugg & Wilding, 1996), have pointed out that functional neuroimaging studies of episodic memory tend to show significantly greater activation in parietal regions for previously studied items that are correctly recognized as old, compared to unstudied items that are correctly identified as new. Furthermore, some studies have suggested that parietal activations are stronger in cases where one has a vivid, clear recollection (i.e., remembering) of an item and the contextual details surrounding it, as opposed to a more intuitive feeling of familiarity (i.e., knowing that the stimulus has been encountered recently without awareness of the context in which it appeared; Tulving, 1985). These findings have led some researchers to suggest that parietal cortex plays a heretofore underappreciated role in episodic memory. Such an assertion is provocative, however, because memory is not a function that has traditionally been ascribed to the parietal lobe. Classic texts on the functions of parietal cortex have made scant mention of memory (e.g., Critchley, 1953 and Luria, 1966), and those on the neuropsychology of memory have said little about the parietal lobe (e.g., Luria, 1976). In the interest of seeking convergence with the functional neuroimaging data, we examined the literature on the effects of parietal lesions on memory, and we report six cases of focal parietal damage, examining memory processes in detail.
نتیجه گیری انگلیسی
We sought to examine the assertion that the lateral parietal region plays a previously underappreciated role in episodic memory. Although functional neuroimaging data support this assertion, there are very few patient lesion data on this matter. Consistent with clinical impressions and previous studies, we found that patients with focal lateral parietal damage did not have amnesia, yet the patients did show evidence of disrupted recollection. This may be due to attentional or working memory effects at retrieval, or effects on retrieval of contextual information. At present there is insufficient evidence to indicate which of these processes are involved. These data, although preliminary, warrant further research on the ways in which the parietal region might support memory. Future work will have to take into account several outstanding questions. First, to what degree are the effects of parietal damage on memory similar to, or different from, damage to other regions? In the present study, we found that parietal patients did not show a severe memory impairment like that which follows bilateral medial temporal lobe damage. However, it would be useful in future work to contrast the effects of parietal damage with damage to other regions that appear to be involved in memory, and are connected to the lateral parietal region, such as prefrontal cortex. Second, do different subregions of the lateral parietal area have specialized functions (as suggested by Wagner et al., 2005)? Note that this question is currently under investigation with respect to the prefrontal cortex: for example, some subregions of prefrontal cortex may be more important for recollection compared to familiarity (e.g., Duarte, Ranganath, & Knight, 2005; Eldridge et al., 2000 and Henson et al., 1999; Wheeler & Buckner, 2004; Wheeler & Stuss, 2003; for a review, see Skinner & Fernandes, 2007), but the exact brain-behavior pattern one finds may depend on exactly what kind of paradigm one uses (cf. Ciaramelli & Ghetti, 2007; Duarte et al., 2005; Levine, Freedman, Dawson, Black, & Stuss, 1999). In the present study, we examined only a small group of patients, making it difficult to say for certain whether different subregions of the lateral parietal zone play different roles in memory. Third, do the left and right hemispheres make different contributions, and if so, do they differ along material- or process-specific lines? In the current study, all but one of our patients had left hemisphere damage, and the tasks that we used were mostly verbal. Considering the possibly greater role of right compared to left parietal cortex in visual attention, there may be some hemispheric specialization in memory processes. Although a larger scale patient study could help answer this question, it would also be useful to have a comprehensive meta-analysis of single-trial fMRI studies of episodic memory. Such a meta-analysis could contrast activation patterns seen, for example, with verbal compared to non-verbal stimuli, or during the encoding compared to the retrieval phase, in order to help guide lesion research. The reviews of parietal activation by Naghavi and Nyberg (2005), Skinner and Fernandes (2007), and Wagner et al. (2005) were each relatively selective, and none considered potential hemispheric differences in depth. Although lesion studies are essential for determining whether a particular brain region is critical for a particular cognitive process, the lesion method is far from perfect. Interpretation of lesion data is complicated by many factors, including diaschisis (when damage to one area has effects on other areas that are connected to it), post-injury reorganization, and degeneracy (where a lesion causes a shift from one brain region or mental process to another, with no apparent effect on behavior). Thus, a particularly fruitful technique may be to combine functional neuroimaging and lesion approaches where patients’ lesions are well-defined, and memory performance is studied in depth (Price & Friston, 2002). Another potentially useful strategy is to induce temporary functional lesions using transcranial magnetic stimulation, although the behavioral effects of this method tend to be quite small (for an initial study, see Rossi et al., 2006). Because every method in cognitive neuroscience has its own strengths and weaknesses, using a combination of them is crucial to developing a more sophisticated picture of how episodic memory is supported by the brain.