Abstract
An Asian spice, Szechuan pepper (sanshool), is well known for the tingling sensation it induces on the mouth and on the lips. Electrophysiological studies have revealed that its active ingredient can induce firing of mechanoreceptor fibres that typically respond to mechanical vibration. Moreover, a human behavioral study has reported that the perceived frequency of sanshool-induced tingling matches with the preferred frequency range of the tactile rapidly adapting (RA) channel, suggesting the contribution of sanshool-induced RA channel firing to its unique perceptual experience. However, since the RA channel may not be the only channel activated by sanshool, there could be a possibility that the sanshool tingling percept may be caused in whole or in part by other sensory channels. Here, by using a perceptual interference paradigm, we show that the sanshool-induced RA input indeed contributes to the human tactile processing. The absolute detection thresholds for vibrotactile input were measured with and without sanshool application on the fingertip. Sanshool significantly impaired detection of vibrations at 30 Hz (RA channel dominant frequency), but did not impair detection of higher frequency vibrations at 240 Hz (Pacinian-corpuscle (PC) channel dominant frequency) or lower frequency vibrations at 1 Hz (slowly adapting 1 (SA1) channel dominant frequency). These results show that the sanshool induces a peripheral RA channel activation that is relevant for tactile perception. This anomalous activation of RA channels may contribute to the unique tingling experience of sanshool.
Highlights
Szechuan pepper, a widely used spice in the cuisine of many Asian countries, is well known for the unique tingling and numbing sensation it induces on the tongue and on the lips [1, 2]
We showed that the application of sanshool on the finger interferes with perceptual processing of rapidly adapting (RA)-preferred frequency range mechanical input (30Hz vibration) on that finger
Consistent with the previous neurophysiological and behavioural studies, our result indicates that, among the three mechanical tactile channels, RA channel is the major channel activated by sanshool, and which impacts on the further tactile information processing
Summary
A widely used spice in the cuisine of many Asian countries, is well known for the unique tingling and numbing sensation it induces on the tongue and on the lips [1, 2]. This “tingling” is experienced as a tactile phenomenon. The question is how this sensation is elicited without any physical touch, and which aspect of tactile processing it taps into. Previous studies in mice have shown that the bioactive component of Szechuan pepper, hydroxyl-a-sanshool (hereafter sanshool), elicits chemical events within the receptor.
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