Cerebral localisation function from the input of single mechanoreceptive units in man.

The accuracy of the cerebral localisation function from the input of single mechanoreceptive units was studied in the hand and forearm of human subjects by means of microneurography and intraneural microstimulation (INMS). The mean distance separating the projected field of a sensation evoked by INMS at liminal amplitude from the receptive field of the activated unit (interfield distance, or IFD) was found to vary from 2.6 mm for SA I units in the fingertips to 23.4 mm for SA I units in the forearm. A less pronounced proximodistal IFD gradient was found for quickly adapting units. IFD values for each skin region were comparable with those obtained by a point localisation test directly on the skin. This indicates that functional gradients exist for inputs from single mechanoreceptive units, and that stimulus localisation hardly improves when numerous units are coactivated.