Temperature sensitivity of the body surface over the life span.

Detection thresholds to warming and cooling were measured in 13 regions of the body in 60 adults aged between 18 and 88 years. From these thresholds were constructed maps of thermal sensitivity homologous to body maps of spatial acuity (in the older literature two-point discrimination), long known to the somatosensory scientist. Maps of cold and warm sensitivity for young, middle-aged and elderly adults, show how sensitivity changes with age in the various body regions. Three characteristics emerge, irrespective of age: (1) sensitivity varies approximately 100-fold over the body surface. The face, especially near the mouth, is exquisitely sensitive, the extremities, by comparison, poor, other regions, intermediate. (2) All body regions are more sensitive to cold than to warm. (3) The better a region is at detecting cold, the better it is at detecting warm. With age, thermal sensitivity declines. The greatest changes take place in the extremities, especially the foot, where thresholds often become too large to measure. Central regions give up their sensitivity with age more slowly, and even (as in the lips) inconsequentially. Similar age-related changes have also previously been shown to characterize spatial acuity.