Investigation of cortical activation patterns in response to the inter-digit vibrotactile stimulation

Mechanosensation includes the detection of mechanical stimuli from mechanoreceptors and sensory signal transduction to the somatosensory cortex through neural afferents. Previous studies reported the sensory signals of flutter (5-50 Hz) and vibration (50-400 Hz) traveled through separated neural afferents of rapidly adapting type 1 (RA) and rapidly adapting type 2 (PC) respectively, and they activated the primary (S1) and secondary (S2) somatosensory cortices with spatially distinct patterns. In this study, we investigated the cortical activation patterns of S1 and S2 in response to flutter and vibration delivered onto the tips of index (D2) and little (D5) digits using functional magnetic resonance imaging (fMRI). We demonstrated that D2 provided more apparent cortical activation patterns that the event of flutter stimulation elicited contralateral S1 and bilateral S2 activation while the event of vibration stimulation mainly elicited bilateral S2 activation due to the somatotopic neural projection mechanisms of the RA and PC afferents and the density distribution of mechanoreceptors.