A new device for tactile stimulation during fMRI

Standardized somatosensory stimulation of the face during functional MRI is technically demanding due to the high magnetic field of the MRI scanner and the confined geometry of the head coil. We developed a new computer-controlled MR-compatible stimulation device for mapping somatosensory-evoked brain activations during fMRI. The device employs von Frey-filaments which are commonly used for quantitative sensory testing (QST) to deliver punctate tactile stimuli to the face and other body surfaces with a high spatiotemporal accuracy. Such stimuli were applied to the ipsilateral face and hand of eight volunteers during two different experimental designs to explore the feasibility of the new stimulator for somatosensory mapping. Tactile stimulation activated a distributed neural network including primary (S1) and secondary (S2) somatosensory areas as well as the premotor cortex and the thalamus. An event-related experimental design yielded S1 activation in all subjects despite a smaller total number of stimuli compared to a blocked design where S1 activation was not consistently found in three subjects. In individuals where S1 was significantly activated during both experimental conditions, the punctate tactile stimuli allowed discriminating the face and the hand representation in S1. We conclude that the novel stimulation device appears to be a valuable tool for mapping somatosensory representations. The data suggest that an event-related study design could be beneficial as it better controls for confounding factors such as anticipation, habituation and attention.