Tactile and pain mechanical sensitivity of the human hand
The human hand has a refined mechanical sensitivity, allowing it to play crucial roles in tactile exploration and object manipulation. Despite its fundamental and clinical relevance, a comprehensive characterization of mechanical sensitivity across the human palm is still lacking. Here, we mapped the spatial distribution of innocuous and noxious mechanical sensitivity across the palmar surface of the human hand. We examined 66 hands from 33 healthy adults, dividing the palm into 27 areas, in each of which we measured the mechanical detection threshold, the mechanical pain threshold and the pain intensity evoked by a standard 300 g pinprick stimulus. We found distal areas (i.e., fingertips) to exhibit higher tactile sensitivity than proximal areas (i.e., the wrist). Notably, the sensitivity to innocuous and noxious mechanical stimuli were inversely correlated across areas, such that areas with higher tactile sensitivity displayed higher pain thresholds. In addition, the dominant hand was less sensitive than the non-dominant one, and women displayed higher sensitivity than men. Together, this work provides the first detailed spatial characterization of mechanical sensitivity across the human hand and introduces a systematic methodology for its assessment. These findings set the stage for future studies of the neurophysiological mechanisms of touch and pain in the human hand and for clinical research into pathological conditions involving the altered hand sensitivity.