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Sylvain Houle
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Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2000) 12 (1): 163–173.
Published: 01 January 2000
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Large-scale networks of brain regions are believed to mediate cognitive processes, including episodic memory. Analyses of regional differences in brain activity, measured by functional neuroimaging, have begun to identify putative components of these networks. To more fully characterize neurocognitive networks, however, it is necessary to use analytical methods that quantify neural network interactions. Here, we used positron emission tomography (PET) to measure brain activity during initial encoding and subsequent recognition of sentences and pictures. For each type of material, three recognition conditions were included which varied with respect to target density (0%, 50%, 100%). Analysis of large-scale activity patterns identified a collection of foci whose activity distinguished the processing of sentences vs. pictures. A second pattern, which showed strong prefrontal cortex involvement, distinguished the type of cognitive process (encoding or retrieval). For both pictures and sentences, the manipulation of target density was associated with minor activation changes. Instead, it was found to relate to systematic changes of functional connections between material-specific regions and several other brain regions, including medial temporal, right prefrontal and parietal regions. These findings provide evidence for large-scale neural interactions between material-specific and process-specific neural substrates of episodic encoding and retrieval.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2000) 12 (1): 197–206.
Published: 01 January 2000
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Positron emission tomography (PET) was used to investigate the hypothesis that older adults' difficulties with temporal-order memory are related to deficits in frontal function. Young (mean 24.7 years) and old (mean 68.6 years) participants studied a list of words, and were then scanned while retrieving information about what words were in the list (item retrieval) or when they occurred within the list (temporal-order retrieval). There were three main results. First, whereas the younger adults engaged right prefrontal regions more during temporal-order retrieval than during item retrieval, the older adults did not. This result is consistent with the hypothesis that context memory deficits in older adults are due to frontal dysfunction. Second, ventromedial temporal activity during item memory was relatively unaffected by aging. This finding concurs with evidence that item memory is relatively preserved in old adults and with the notion that medial temporal regions are involved in automatic retrieval operations. Finally, replicating the result of a previous study (Cabeza, R., Grady, C. L, Nyberg, L., McIntosh, A. R., Tulving, E., Kapur, S., Jennings, J. M., Houle, S., & Craik, F. I. M., 1997), the old adults showed weaker activations than the young adults in the right prefrontal cortex but stronger activations in the left prefrontal cortex. The age-related increase in left prefrontal activity may be interpreted as compensatory. Taken together, the results suggest that age-related changes in brain activity are rather process- and region-specific, and that they involve increases as well as decreases in neural activity.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (1998) 10 (3): 293–302.
Published: 01 May 1998
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One of the important questions cognitive theories of reasoning must address is whether logical reasoning is inherently sentential or spatial. A sentential model would exploit nonspatial (linguistic) properties of representations whereas a spatial model would exploit spatial properties of representations. In general terms, the linguistic hypothesis predicts that the language processing regions underwrite human reasoning processes, and the spatial hypothesis suggests that the neural structures for perception and motor control contribute the basic representational building blocks used for high-level logical and linguistic reasoning. We carried out a [ 15 O] H 2 O PET imaging study to address this issue. Twelve normal volunteers performed three types of deductive reasoning tasks (categorical syllogisms, three-term spatial relational items, and three-term nonspatial relational items) while their regional cerebral blood flow pattern was recorded using [ 15 O] H 2 O PET imaging. In the control condition subjects semantically comprehended sets of three sentences. In the deductive reasoning conditions subjects determined whether the third sentence was entailed by the first two sentences. The areas of activation in each reasoning condition were confined to the left hemisphere and were similar to each other and to activation reported in previous studies. They included the left inferior frontal gyrus (Brodmann areas 45, 47), a portion of the left middle frontal gyrus (Brodmann area 46), the left middle temporal gyrus (Brodmann areas 21, 22), a region of the left lateral inferior temporal gyrus and superior temporal gyrus (Brodmann areas 22, 37), and a portion of the left cingulate gyrus (Brodmann areas 32, 24). There was no significant right- hemisphere or parietal activation. These results are consistent with previous neuroimaging studies and raise questions about the level of involvement of classic spatial regions in reasoning about linguistically presented spatial relations.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (1997) 9 (2): 254–265.
Published: 01 March 1997
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The purpose of this study was to directly compare the brain regions involved in episodic-memory recall and recognition. Changes in regional cerebral blood flow were measured by positron emission tomography while young healthy test persons were either recognizing or recalling previously studied word pairs. Reading of previously nonstudied pairs served as a reference task for subtractive comparisons. Compared to reading, both recall and recognition were associated with higher blood flow (activation) at identical sites in the right prefrontal cortex (areas 47, 45, and 10) and the anterior cingulate. Compared to recognition, recall was associated with higher activation in the anterior cingulate, globus pallidus, thalamus, and cerebellum, suggesting that these components of the cerebello-frontal pathway play a role in recall processes that they do not in recognition. Compared to recall, recognition was associated with higher activation in the right inferior parietal cortex (areas 39, 40, and 19), suggesting a larger perceptual component in recognition than in recall. Contrary to the expectations based on lesion data, the activations of the frontal regions were indistinguishable in recall and recognition. This finding is consistent with the notion that frontal activations in explicit memory tasks are related to the general episodic retrieval mode or retrieval attempt, rather than to specific mechanisms of ecphory (recovery of stored information).