The role of cutaneous mechanoreceptors in thermal sensation and pain.

The functional behavior of slowly adapting cutaneous mechanoreceptors under combined thermal-mechanical stimulation was investigated by single-unit recordings from the lumbar dorsal roots of the cat. Increased sensitivity to bimodal stimulation was observed in 24 of the 28 units studied, employing stimulus-response functional behavior as the basis for judgment. Low-threshold receptors generally did not exhibit increased spontaneous firing as accompaniment to heightened sensitivity, while such enhanced basal activity was usually observed in moderate-threshold units in addition to increased reactivity. Information theory calculations performed on these stimulus-response data revealed that 15 of the 24 "heat-sensitive" receptors were additionally characterized by an enhanced ability to transmit neural information under bimodal stimulation. These results were interpreted as supporting pattern theories of pain as opposed to the concept of receptor specificity. No contradiction was observed, however, between the present results and those of other investigators. The present conclusions derive from new criteria for thermal reactivity based upon innovative stimulus conditions.