SOMATOTOPIC LOCALIZATION OF THERMAL STIMULI .1. A COMPARISON OF WITHIN-DERMATOMAL VERSUS ACROSS-DERMATOMAL SEPARATION OF INNOCUOUS THERMAL STIMULI

Fourteen healthy subjects (4 males, 10 females) were asked to localize a thermal stimulus applied to the left distal forearm. Two temperatur e-controlled probes (1.2-cm(2) area each) were strapped to the forearm , separated by 8 cm. The probes were positioned in one of three ways: (1) longitudinally within the C6 dermatome, (2) longitudinally within the C8 dermatomes, and (3) transversely with one probe within the C6 a nd one probe within the C8 dermatome. For any given stimulus configura tion, cooling stimuli were localized significantly better than warming stimuli. For both warming and cooling, the transdermatomal configurat ion (transversely separated probes) provided significantly better loca lization than the intradermatomal configuration (longitudinally separa ted probes). Thus, the anisotropy that has been described for tactile spatial acuity is also present for thermal localization. These results suggest that cutaneous somatotopic information is integrated similarl y for both tactile and thermal stimuli, but differently within versus across dermatomes.