The Relation Between Stimulus and Discharge in a Rapidly Adapting Touch Receptor

A quantitative experimental analysis was made in decerebrate toads of the relation between stimulus and discharge in touch receptors of the common rapidly adapting type. The stimuli consisted of mechanical pulses of variable slope, amplitude and duration. Recording was made from single afferent fibres in the dorsal root. The impulse frequency of the discharge from the very rapidly adapting receptors, and of the dynamic discharge from the less rapidly adapting receptors, varied with the gradient of the stimulus in a characteristic way. When the rate of the displacement was successively increased from the minimum effective value (critical slope), the impulse frequency was low at first, and then rose as a logarithmic function of the displacement rate (Fig. 2, 3, 5 and 6). The range of rates in which the change in frequency occurred was called the optimal slope range of the receptor. The impulse frequency was independent of the amplitude of the displacement in the very rapidly adapting receptors (Fig. 1 and 3 B), and only partially related to it in the less rapidly adapting ones. The demonstrated relation between displacement rate and discharge frequency constitutes a basis for an exact reproduction of the temporal characteristics of the stimuli and may be of primary importance for tactile discrimination.