Proximal receptors and the mechanical stimulation of the fingers: a somatosensory evoked potential study

To characterize scalp responses to mechanical stimulation of the fingers and evaluate the contribution of different receptors.

Somatosensory evoked responses to mechanical stimulation of the right third finger were recorded from a P3-P4 montage (n = 15) and from a F3-P4 montage (n = 9) as well as after electrical stimulation (n = 9). Responses after mechanical stimulation of the distal region of the finger, with the hand at different positions, were also recorded (n = 8). Complementary experiments in a small number of individuals included EMG and accelerometer recordings as well as anaesthesia of the finger.

Scalp responses characterized by an initial sequence of waves, here called NI-PI-NII, were recorded from the P3-P4 montage. Mean peak latencies were 20, 23 and 26 ms, respectively; electrical stimulation of the same region evoked an initial negativity (mean peak latency 23 ms). EMG recordings suggested the involvement of different receptors in response to electrical and mechanical stimulation. Accelerometer recordings showed the spread of a sizable mechanical wave at the forearm. Anaesthesia did not change the responses to mechanical stimulation.

Relatively small mechanical stimuli applied at distal phalanxes may activate proximal receptors which generate scalp recorded responses that may completely occlude the contribution of the distal receptors.