The effect of short-term peripheral nerve stimulation (PNS) on sensitivity and hand motor performance in healthy aging : a pilot study

Abstract

It is known that healthy aging is accompanied by sensorimotor slowing in a wide range of speeded tasks (Salthouse 2000) and that tactile perception decreases over life span (Woodward, 1993; Stevens & Choo, 1996). Long-term PNS (2h) has already shown to increase the size of MEPs evoked by TMS in hand muscles (Ridding et al., 2000). A similar long-term PNS protocol has shown to induce improvements in motor performance in stroke patients (Celnik et al., 2009). However, while this long-term protocol seems relevant for neurorehabilitation, we are focusing on a comfortable short-term therapy. We hypothesize that short-term PNS would lead to improved sensitivity and/or motor function of the dominant hand. Methods Twenty-five right-handed neurologically intact elderly (6M/19F; age: 73.24 ± 4.97; Oldfield: 95.76 ± 8.15; MMSE > 26) participated in a double-blind sham controlled cross-over study. The intervention consisted of 20min PNS (square wave, 10 Hz, pulse width: 0.8ms, cathode proximal) on the median and ulnar nerve of the wrist. Semmes-Weinstein monofilaments (SWM) were used for a sensitivity training during the intervention (TENS/SHAM). During the training feedback about the perception of the touch was provided. Before and after the intervention sensitivity and motor performance was evaluated using respectively the SWM and the JebsenTaylor Hand Function Test (JTHFT). Results Hand motor performance The intervention showed no significant effect on total JTHFT time over time (P = 0.088). This finding was also found for every single subtest (turning over cards, picking up small objects and placing them in a can, picking up small objects with a teaspoon and placing them in a can, stacking checkers, moving large light cans, moving heavy cans and writing tasks; all, P > 0.05). Within both the TENS and the SHAM group there was no significant time-effect for total JTHFT time (P > 0.05). In both groups, every single subtest revealed only a significant time-effect for the subtests turning over cards (P < 0.05) and moving heavy cans (P < 0.05). Sensitivity The intervention showed no significant effect of TENS or SHAM on sensitivity over time (P = 0.523). Within the TENS and SHAM condition no time-effect was found (both, P > 0.05). Conclusion The short-term PNS protocol used in this study did not reveal any significant improvements in sensitivity and/or motor function of the dominant hand. Future experiments will mainly focus on manipulating the stimulation parameters (pulse width, frequency, electrode placement, intensity, wave form, etc.) since these parameters seem to play a crucial role in the size and the direction of the effect.