Cortical activation during a spatiotemporal tactile comparison task.

Tactile sensory memory is needed to infer shape or motion from the spatiotemporal pattern of sensory input during manual exploration. Here we applied triplets of pressure pulses to the fingertips of subjects who were asked to respond when successive triplets were the same (COMPARE task) or when a particular stimulus was included in a triplet (CONTROL task). Stimulus sequences (30 s) alternated with rest blocks (30 s) and functional magnetic resonance images (fMRIs) were acquired in a 1.5-T scanner. During the COMPARE task, we found enhanced activation in inferior parietal cortex, supplementary motor area (SMA), and right dorsolateral prefrontal cortex (DLPFC). Activation of DLPFC is likely to be related to the attempt to memorize the stimulus sequences and activations of SMA and inferior parietal cortex to the analysis of temporospatial tactile patterns and, more generally, to guidance of haptic exploration. In addition, task-specific activation was seen in anterior cingulate gyrus, possibly related to the high mental effort required by the comparison task. Our rhythmic tactile stimulus as such, without any task-specific enhancement, activated also left cerebellum and (mainly left) putamen, supporting the idea that these structures are related to perception of temporal order of tactile stimuli.