Parametric fMRI activation of cortical regions during visual speed discrimination in healthy and diabetic patients J Duarte, M Raimundo, M Castelo-Branco |
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Visual Neuroscience Laboratory, IBILI, Faculty of Medicine, University of Coimbra, Portugal
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| Here we studied the BOLD functional magnetic resonance imaging (fMRI) responses of 49 healthy subjects during a speed discrimination visual task. The participants detected the faster of two dots, one in each visual hemi-field (moving with 4 possible speed differences). Speed discrimination recruited parietal and occipital regions in relation to stimulus physical characteristics and hMT and frontal regions modulated with task difficulty. BOLD responses were parametrically modulated such that conditions with higher speed differences showed higher activation in sensory regions and lower activation regions related to perceptual decision (beta values per condition tested with ANOVA, p<0.05). Furthermore, a contrast comparing the response to speed differences in the same visual hemi-field revealed statistically significant activation in the contra-lateral insula, suggesting its important role in interhemispheric integration of motion information. We also studied 36 patients with type 2 diabetes in whom we observed some of the same regions identified in the healthy brain. Whereas in the latter a linear parametric effect of speed discrimination was consistently found, this was not identified in type 2 diabetic patients, suggesting that these might have a different hemodynamic response function. |
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