Augmented visual feedback counteracts the effects of surface muscular functional electrical stimulation on physiological tremor.
BACKGROUND
Recent studies suggest that surface muscular functional electrical stimulation (FES) might suppress neurological upper limb tremor. We assessed its effects on upper limb physiological tremor, which is mainly driven by mechanical-reflex oscillations. We investigated the interaction between FES and augmented visual feedback, since (a) most daily activities are performed using visual cues, and (b) augmented visual feedback exacerbates upper limb tremor.


METHODS
10 healthy subjects (23.4 ± 7.7 years) performed 2 postural tasks with combinations of FES (4 sites; frequency of stimulation: 30 Hz; pulse width: 300 microsec; range of current delivered 10-34 mAmp) and augmented visual feedback.


RESULTS
Spectral analysis of tremor showed a decrease of power spectral density to 62.18% (p = 0.01), of the integral in the 8-12 Hz frequency band to 57.67% (p = 0.003), and of tremor root mean square (RMS) to 57.16% (p = 0.002) during FES, without any changes in tremor frequency. Augmented visual feedback blocked the beneficial effect of FES, as confirmed by power spectral analysis (p = 0.01). We found a statistically significant interaction between augmented visual feedback and electrical stimulation (p = 0.039).


CONCLUSIONS
Augmented visual feedback antagonizes the effects of FES on physiological tremor. The absence of changes of peak frequency argues against an effect of FES on mechanical properties of the upper limb.
Unité d'Etude du Mouvement (UEM), ULB-Erasme, 808 Route de Lennik, 1070, Bruxelles, Belgium. giulianagrim@yahoo.it.
Giuliana
G
Grimaldi
Alfredo
A
Fernandez
Mario
M
Manto
D002531:Cerebellum / Q000502:physiology*; D004558:Electric Stimulation; D004576:Electromyography; D056228:Feedback, Sensory / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D011597:Psychomotor Performance / Q000502:physiology; D014202:Tremor / Q000503:physiopathology*; D055815:Young Adult