Independence of spatial and temporal tuning in the NP I cutaneous mechanoreceptor system

Abstract

Results from a previous study that measured tactile detection thresholds for spatiotemporal sinusoids suggest that the spatial and temporal tuning of the P and NP I cutaneous mechanoreceptor systems are independent. In other words, provided that the spatial configuration of a vibratory stimulus is independent of temporal frequency, changing the spatial configuration should not change the shape of the temporal tuning curve of either system. To test this hypothesis for the NP I system, vibrotactile thresholds were measured as a function of temporal frequency (10, 12, 15, 20, 25, 30, 40, 55, 80, 100, 175, and 250 Hz) for 200-ms stimuli delivered to the thenar eminence via a 0.75-cm2 circular contactor, with and without a rigid surround. At frequencies where the threshold was mediated exclusively by the NP I system, the presence of a rigid surround did not significantly alter the shape of the temporal tuning curve, but did change the overall sensitivity. That is, NP I thresholds were uniformly higher without the surround than with the surround. Similar results were obtained when the experiment was repeated on the forearm. The observed invariance in the shape of the low-frequency tuning curve is consistent with the spatiotemporal independence hypothesis, but is consistent with conclusions from prior studies. The apparent discrepancy will be discussed.