Diversity of coding profiles of mechanoreceptors in glabrous skin of kittens.
We examined stimulul-response (S-R) profiles of 35 single mechanoreceptive afferent units having small receptive fields in glabrous forepaw skin of 24 anesthetized domestic kittens. Single unit activity was recorded with tungsten microelectrodes from cervical dorsal root ganglia. The study was designed to be as quantitatively descriptive as possible. We indented each unit's receptive field with a broad battery of simple, carefully controlled stimuli whose major parameters, including amplitude, velocity, acceleration, duration, and interstimulus interval were systematically varied. Stimuli were delivered by a small probe driven by a feedback-controlled axial displacement generator. Single unit discharge data were analyzed by a variety of direct and derived measures including dot patterns, peristimulus histograms, instantaneous and mean instantaneous firing rates, tuning curves, thresholds for amplitude and velocity, adaptation rates, dynamic and static sensitivities, and others. We found that with respect to any of the S-R transactions examined, the properties of our sample of units were continuously and broadly distributed. Any one unit might exhibit either a slow or rapid rate of adaptation, or might superficially appear to preferentially code a single stimulus parameter such as amplitude or velocity. But when the entire range of responsiveness of units to the entire stimulus battery was surveyed by a variety of analytic techniques, we were unable to find any justifiable basis for designation of discrete categories of S-R profiles. Intermediate response types were always found, and in general, all units were both broadly tuned and capable of responding to integrals of several stimulus parameters, our data argue against the usefulness of evaluating a unit's S-R coding capabilities by means of a limited ste of stimulation of response analysis procedures.
D000222:Adaptation, Physiological; D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D002415:Cats; D004594:Electrophysiology; D005552:Forelimb / Q000294:innervation; D005727:Ganglia, Spinal / Q000166:cytology / Q000502:physiology*; D008465:Mechanoreceptors / Q000502:physiology*; D009431:Neural Conduction; D012867:Skin / Q000294:innervation*; D013997:Time Factors