Functional Mapping of the Human Somatosensory Cortex with Echo‐Planar MRI

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Abstract
The somatotopical organization of the human somatosensory cortex was analyzed with echo‐planar imaging at 1.5 Tesla, utilizing deoxyhemoglobin as an endogenous contrast medium. Scrubbing stimulation at a frequency of 3 Hz was applied to one of three cutaneous areas: toes, fingertips, and tongue tip. Parasagittal echo‐planar slices were obtained every 2 s. We found focal bands of increased signal intensity (4% on average) during the stimulation, with a rise time of 2–6 s. These activated bands were located on the contralateral postcentral gyrus. The cortical responses from the three stimulation sites were anatomically distinct and organized medially‐to‐laterally in the order of toes, fingertips, and tongue tip.