SPATIAL SUMMATION OF PERCEIVED PRESSURE, SHARPNESS AND MECHANICALLY EVOKED CUTANEOUS PAIN

Psychophysically, spatial summation can be demonstrated as a decrease in threshold accompanying an increased field of stimulation. The prese nt study examined to what extent different mechanically evoked percept s (pressure, sharpness, and pain) show spatial summation. Various prob es were used to apply prescribed forces to the dorsal surface of the d igits of 19 healthy subjects. The threshold fdr three perceptual quali ties showed differing degrees of spatial summation: sharpness showed n o statistically significant spatial summation; pain demonstrated some significant summation (46% on average); pressure showed the greatest d egree of spatial summation (76% on average). The lack of significant s patial summation for sharpness threshold is consistent with the theory that perceived sharpness can be evoked by near threshold activity of a single nociceptor. The modest amount of spatial summation for pain i mplies that distinctly suprathreshold activation of nociceptors is req uired for mechanically evoked pain perception, and such input summates centrally, but not completely. The greater spatial summation observed for pressure vs. pain thresholds implies a greater degree of central summation for slowly adapting mechanoreceptors vs. nociceptors.