Patterns of lateral sensory cortical activation determined using functional magnetic resonance imaging

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Abstract
Functional magnetic resonance (fMR) imaging was performed in human volunteers to determine the lateral perisylvian cortical areas activated by innocuous cutaneous stimulation. Eight volunteers who underwent 53 separate experiments form the basis of this report. Eight contiguous coronal slices were obtained using echoplanar fMR imaging techniques while participants were at rest and while somatosensory activation stimuli consisting of vibration or air puffs were delivered to various body areas. The data were analyzed using Student's t-test and cluster analysis to determine significant differences between the resting and activated states. The findings were as follows: the areas in the lateral cortex activated by the stimuli were the primary sensory cortex (SI), the second somatosensory area (SII), the insula, the superior parietal lobule, and the retroinsular parietal operculum (RIPO). Somatotopy was demonstrable in SI but not in the other areas identified. There was a surprisingly low correlation between the amount of cortex activated in the various areas, which could mean separate inputs and functions for the areas identified. The highest correlation was found between activity in SII and RIPO (0.69). The authors maintain that fMR imaging can be used to identify multiple lateral somatosensory areas in humans. Somatotopy is demonstrated in SI but not in the other lateral cortical sensory areas. The correlations between the amounts of cortex activated in the different lateral sensory areas are low. Recognition of the multiple lateral sensory areas is important both for understanding sensory cortical function and for safe interpretation of studies designed to identify the central sulcus by activating SI.