Somatosensory evoked fields to large-area vibrotactile stimuli

We describe a method to apply large-area vibrotactile stimuli, based on a vibrating balloon, on the palms of both hands during evoked response studies. Magnetoencephalographic (MEG) signals were recorded with a whole-scalp neuromagnetometer from six healthy subjects while they held their hands on a balloon which was made to vibrate by delivering tones to it through a loudspeaker and a tube. The 200 Hz stimuli, presented once every 1 or 2 s in separate sessions, elicited prominent and replicable somatosensory evoked fields (SEFs) and also auditory evoked fields (AEFs) due to the concomitant sound. Source modelling allowed reliable differentiation between bilateral activation of the primary somatosensory (SI) cortices (peaks at 46-61 ms after the stimulus onset) and of the supratemporal auditory cortices (peaks at 104-126 ms). These simple vibrotactile stimuli could be useful for rapid and reliable identification of the somatosensory and auditory cortices, for example in presurgical evaluation of children.