Acute impairment of the sensitivity of skin mechanoreceptive units caused by vibration exposure of the hand

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Abstract
The thresholds of single mechanoreceptive afferent units, innervating the glabrous skin of the human hand to sinusoidal skin indentations at 2, 20 or 200 Hz were measured before and after 2 min powerful vibration exposures at the same frequencies. The corresponding psychophysical thresholds were measured in collateral experiments while still monitoring the unit responses. An acute but temporary rise in threshold occurred as a consequence of the vibration exposure in three different unit types (FA I, FA II and SA I). A close correlation was found between the neural and psychophysical thresholds with regard to the magnitudes of the shifts and the time courses of the recovery, provided that the thresholds were measured at the appropriate frequencies (i.e. at 200, 20 and 2 Hz while recording from FA II, FA I and SA I units, respectively). It was concluded that the acute impairment of tactile sensibility caused by vibration exposure, as earlier observed in psychophysical studies, most likely can be explained by a depression of the excitability of the mechanoreceptive afferent units.