Evidence of vibrotactile input to human auditory cortex

Low frequency vibrations can be detected by both tactile and auditory systems. The aim of the present study is to find out, by means of whole-scalp magnetoencephalography (MEG), whether vibrotactile stimulation alone would activate human auditory cortical areas. We recorded MEG signals from eleven normal-hearing adults to 200-Hz vibrations (on average 19.5 dB above the individual tactile detection threshold), delivered to right-hand fingertips. All subjects reported a perception of a sound when they touched the vibrating tube, and they reported to perceive nothing when not touching the tube. The vibrotactile stimuli elicited clear and reproducible vibrotactile evoked fields (VTEFs) in ten subjects, whereas no MEG responses were observed when the tube was not touched. First responses to the vibrotactile stimuli, peaking around 60 ms, originated in the primary somatosensory cortex in all subjects. They were followed by activations in the auditory cortices, either bilaterally (N = 5) or unilaterally (N = 5), and by activations in the secondary somatosensory (SII) cortex, either contralaterally (N = 3) or ipsilaterally (N = 4). Both the SII and auditory activations consisted of transient responses at 100-200 ms. Additional auditory sustained activation was identified in nine subjects, either bilaterally (N = 2) or ipsilaterally (N = 7), at 200-700 ms. Our results suggest convergence of vibrotactile input to the auditory cortex in normal-hearing adults, in agreement with results previously obtained in a congenitally deaf adult.