Excitation of receptors in the pad of the cat by single and double mechanical pulses

Abstract

The activity produced in single receptor units, on mechanical stimulation of the cat''s pad, has been recorded. Both the displacement at the beginning and the restoration movement at the end of a mechanical pulse can excite or contribute to the excitation of the receptors. Excitation is determined by an amplitude required for threshold (range 1.5-16.5u) and a critical slope (mean, 1.6 x amplitude required for threshold per millisecond.) Receptive fields have dimensions which are negatively correlated to the minimum threshold. Both the amplitude (u) and the velocity (u/msec) required for threshold increase with distance from the centre of the field; critical slope (amplitude required for threshold (msec) is constant. The initiation of impulses is delayed at the periphery of the field. Major changes in the excitability of a receptor to a test pulse on the main pad often result when a subthreshold conditioning pulse is applied at a second point on the main pad, or even occasionally on a small pad. Comparable changes in excitability can occur even when the conditioning pulse is applied to an area of pad which has been cut out and stuck back. This and other evidence which is presented indicate that the properties of the receptive fields and the interactions may be explained by a mechanical wave that travels across the pad with a velocity of the order of 12m/sec. The results need to be taken into account in considering the coding of information by this population of receptor units. Furthermore, the results indicate that facilitatory and inhibitory functions should not be attributed to central mechanisms until there is reason to exclude the possibility of more peripheral interactions.