Activation in SI and SII: the influence of vibrotactile amplitude during passive and task-relevant stimulation.

Using functional magnetic resonance imaging (fMRI), responses in human somatosensory cortex were quantified in response to changes in the amplitude of peripheral stimulation during (1) passive vibration and (2) an attention-demanding tactile tracking task whereby changes in vibration amplitude were used to guide motor behaviour. Functional MRI was conducted using a scanner operating at 1.5 T, and vibration was delivered to the volar surface of the right index finger with a custom-built magnetomechanical device. Results showed that primary somatosensory cortex (SI) reliably reflects changes in vibration amplitude applied to the finger during passive vibration and also in the presence of a task that modulates the activity in SI. Secondary somatosensory cortex did not reveal any clear relationship with vibration amplitude but was more often activated during the attention demanding tracking task compared with passive vibration. The present study supports an increasing stimulus-response relationship between vibrotactile stimuli and activity in SI that persists during attentive, active states.