Vibrotactile perception thresholds at the sole of the foot: Effects of contact force and probe indentation

Abstract: When using vibrotactile thresholds to investigate neuropathy in the fingers, the indentation of a vibrating probe, and the force applied to a static surround around a vibrating probe, affect thresholds. This study was designed to investigate the effects on vibrotactile perception thresholds at the sole of the foot of probe indentation (i.e. height of a vibrating probe relative to a static surround) and the force applied to the static surround. Thresholds at 20Hz (expected to be mediated by the NP I channel) and at 160Hz (expected to be mediated by the Pacinian channel) were obtained at the hallux (i.e. greater toe) and the ball of the foot on 14 healthy subjects. In one condition, the height of the vibrating probe was varied to 0, 1, 2, 3, and 4mm above a static surround with 4-N force applied to the surround. In a second condition, the force applied to the surround was varied to 1, 2, 3, 4, 5, and 6N while using a probe height of 1mm. Thresholds at 20Hz decreased with increasing probe height from 0 to 1mm but showed no significant variation between 2, 3, and 4mm at either the hallux or the ball of the foot. Thresholds at 160Hz decreased with increasing probe height from 0 to 4mm at both the hallux and the ball of the foot. Thresholds at 20Hz obtained with 1-N surround force were higher than thresholds obtained with 2N, but there was no significant difference with surround forces from 2 to 6N at either the hallux or the ball of the foot. Thresholds at 160Hz were unaffected by variations in surround force at the ball of the foot but tended to decrease with increasing force at the hallux. It is concluded that a vibrating probe flush with a static surround, and a surround force in the range 2–4N, are appropriate when measuring vibrotactile thresholds at the hallux and the ball of the foot with a 6-mm diameter contactor and a 2-mm gap to the static surround. [Copyright &y& Elsevier]