Response of cat cutaneous mechanoreceptors to punctate and grating stimuli

Cat hairy skin type I, type II, and field mechanoreceptor response characteristics were studied by drawing punctate and grating stimuli across a unit's receptive field (RF). Area RF maps were generated with scans covering approximately 1 X 1 cm using different vertical loadings, scan velocities, and scan orientations. The results from stimulating with a 1 g mass, 1 mm diam, rounded-tip punctate probe indicate that type I units display essentially invariant response topographies as a function of stimulus parameters. Type II units, presumably because of their unidirectional stretch sensitivity, showed response differences that were a function of the scan orientation. Field units, although not considered to be important for stimulus feature extraction, also displayed a directionally sensitive response profile. Changing the vertical loading or the scanning velocity of the stimulus had a minimal affect on the resulting RF profiles for any of the units studied. Grating stimuli with periods of 0.25-2.0 mm were scanned over receptors to study their grating discrimination ability. Different scan directions were used to study the directional sensitivity of a unit. Both type I and II units had optimal scan orientations for minimum grating period discrimination. For type I units, the dome orientation pattern and interdome sensitivities seemed to be a factor in determining the scan direction for minimum grating period detection. For type II units it was equivocal whether scanning parallel or orthogonal to the direction of maximum stretch sensitivity was better for grating detection. Grating response results were qualitatively similar to the results reported by others for receptors in the glabrous skin of primates. Both type I and II units could reliably discriminate gratings with periods of 0.75 mm and could marginally discriminate gratings with 0.5-mm periods. Field units were not well represented in this study, but those units that were studied were unable to unambiguously discriminate a 2.0-mm period grating, the largest one used.