Frequency following brain oscillations evoked by vibrotactile stimulation of the distal phalanx in normal subjects

The sensory response upon vibrotactile stimuli is still not entirely understood. Previously, the responses of single units from mechanoreceptive afferents and cortical neurons have been studied. There is a thorough psychophysical literature on judgements of the presence, magnitude, and frequency of vibrotactile stimuli. However, non-invasive recording of evoked responses on the scalp have solely been determined for electrical stimuli. In this study, psychophysical detection thresholds of adult subjects were measured at various mechanical frequencies. These values were found to be consistent with the literature. To measure the frequency following brain responses, stimulus intensities were determined based on psychophysical sensation levels. Data recorded from the somatosensory cortex area via electrodes placed on scalp, were analysed with wavelet transform. The results show that, as the mechanical stimulus intensity was increased, the background activity was suppressed and the frequency-following activity during stimulus period increased. This finding was statistically significant.