Tactile stimulus predictability modulates activity in a tactile-motor cortical network.

Manipulating objects in the hand requires the continuous transformation of sensory input into appropriate motor behaviour. Using a novel vibrotactile device combined with fMRI, the cortical network associated with tactile sensorimotor transformations was investigated. Continuous tactile stimuli were delivered in a random or predictable pattern to the second digit on the right hand of all subjects. To better distinguish sensory and motor processes, subjects were instructed to make proportionate motor gripping responses with their left hand. A consistent cortical network of activation was revealed that included the supplementary motor, dorsal and ventral premotor, posterior parietal, primary and secondary somatosensory and primary motor cortex. Tracking the unpredictable versus predictable tactile stimulus led to greater delays in motor responses and to increased performance errors. Cortical effects due to stimulus predictability were observed in several components of the network, though it was most evident as increased cortical activation in frontal motor regions during tracking of unpredictable tactile stimuli. In contrast to the proposed hypotheses, primary and secondary somatosensory cortices contralateral to tactile input did not reveal enhanced responses during unpredictable tracking. Facilitation during unpredictable tracking was also observed in primary somatosensory cortex contralateral to motor responses, the receptive site for movement-related afference. The present study provides a novel and controlled approach to investigate the loci associated with tactile-motor processing and to measure the task-specific effect of stimulus predictability on network components.