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Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2002) 14 (2): 172–186.
Published: 15 February 2002
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One drawback of functional magnetic resonance imaging (fMRI) is that the subject must endure intense noise during testing. We examined the possible role of such noise on the activation of early visual cortex during visual mental imagery. We postulated that noise may require subjects to work harder to pay attention to the task, which in turn could alter the activation pattern found in a silent environment. To test this hypothesis, we used positron emission tomography (PET) to monitor regional Cerebral Blood Flow (rCBF) of six subjects while they performed an imagery task either in a silent environment or in an “fMRI-like” noisy environment. Both noisy and silent imagery conditions, as compared to their respective baselines, resulted in activation of a bilateral frontoparietal network (related to spatial processing), a bilateral inferior temporal area (related to shape processing), and deactivation of anterior calcarine cortex. Among the visual areas, rCBF increased in the most posterior part of the calcarine cortex, but at level just below the statistical threshold. However, blood flow values in the calcarine cortex during the silent imagery condition (but not the noisy imagery condition) were strongly negatively correlated with accuracy; the more challenging subjects found the task, the more strongly the calcarine cortex was activated. The subjects made more errors in the noisy condition than in the silent condition, and a direct comparison of the two conditions revealed that noise resulted in an increase in rCBF in the anterior cingulate cortex (involved in performance monitoring) and in the Wernicke's area (required to encode the verbal cues used in the task). These results thus demonstrate a nonadditive effect of fMRI gradient noise, resulting in a slight but significant effect on both performance and the neural activation pattern.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2000) 12 (1): 98–109.
Published: 01 January 2000
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This study had two purposes. First, in order to address the controversy regarding activation of the primary visual area (PVA) during visual mental imagery, regional cerebral blood flow (rCBF) was recorded while subjects performed a task that required high-resolution visual mental imagery. Second, in order to discover whether verbal descriptions can engage visual mechanisms during imagery in the same way as visual stimuli, subjects memorized 3D scenes that were visually presented or were based on a verbal description. Comparison of the results from the imagery conditions to a non-imagery baseline condition revealed no activation in PVA for imagery based on a verbal description and a significant decrease of rCBF in this region for imagery based on visual learning. The pattern of activation in other regions was very similar in the two conditions, including parietal, midbrain, cerebellar, prefrontal, left insular, and right inferior temporal regions. These results provide strong evidence that imagery based on verbal descriptions can recruit regions known to be engaged in high-order visual processing.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (1995) 7 (4): 433–445.
Published: 01 October 1995
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We measured normalized regional cerebral blood flow (NrCBF) using positron emission tomography (PET) and oxygen-15-labeled water in eight young right-handed healthy volunteers selected as high-imagers. during 2 runs of 3 different conditions: 1, rest in total darkness 2; visual exploration of a map 3; mental exploration of the same map in total darkness. NrCBF images were aligned with individual magnetic resonance images (MRI), and NrCBF variations between pairs of measurements ( N = 15) were computed in regions of interest having anatomical boundaries that were defined using a three-dimensional (3-D) reconstruction of each subject MRI. During visual exploration, we found bilateral activations of primary visual areas, superior and inferior occipital gyri, fusiform and lingual gyri, cuneus and precuneus, bilateral superior parietal, and angular gyri. The right lateral premotor area was also activated during this task while superior temporal gyri and Broca's area were deactivated. By contrast, mental exploration activated the right superior occipital cortex, the supplementary motor area, and the cerebellar vermis. No activation was observed in the primary visual area. These results argue for a specific participation of the superior occipital cortex in the generation and maintenance of visual mental images.