Clinical neurophysiological study on sensory potential originated from mechanoreceptors

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Various mechanoreceptors may respond to tactile stimulli to the human skin. We investigated sensory potentials from the skin evoked by tactile stimuli with indentations of 300 μm at velocities of 100 (T100) and 400 μm/ms (T400) applied to the tip (FT) and the proximal phalanx of digit III (PP) and the thenar eminence (Pm) of 10 healthy volunteers. We compared with responses after electrical stimulation at FT.Compound sensory action potentials (CSAPs) were recorded from the median nerve through needle electrodes at wrist and elbow. The maximal sensory conduction velocities (SNCVs) between wrist and elbow were similar with electrical and T400 stimulation, but on average were 15% lower with T100 stimulation (P<0.001). With both indentation velocities, SNCVs were similar regardless of stimulation sites. Amplitudes of tactile CSAPs with FT stimulation were 1-2 μV at T400 and 0.3-0.4μV at T100. The CSAP areas evoked by T100 stimulation showed a reduction from fingertip to proximal finger to palm (P<0.05-0.005) whereas those obtained with T400 stimulation showed a reduction only at palm (P<0.05). The results support that fast indentation at 400 μm/ms activated deeply placed Pacinian corpuscles as well as superficially situated Meissner corpuscles, whereas the slower indentation at 100 μm/ms activated primarily Meissner corpuscles.