Perceptual improvement following repetitive sensory stimulation depends monotonically on stimulation intensity.

BACKGROUND

Electrical repetitive sensory stimulation (rSS) is a direct and effective means of inducing plasticity processes in human beings, and is increasingly being used as a therapeutic intervention. Suprathreshold intensities induce beneficial effects on tactile perception and sensorimotor abilities. However, it is not known whether there is an optimal range of stimulus intensity.

METHODS

We investigated the effect of varied intensities (low, 1.19 ± 0.07 mA; intermediate, 3.33 ± 0.27 mA; and high, 4.42 ± 0.56 mA) on the outcome of a 30-minute electrical rSS applied to the index finger (intermittent high-frequency stimulation, 20 Hz and interburst interval, 5 seconds) in three groups (n = 10 each) of participants. As a marker of perceptual changes, we measured tactile spatial two-point discrimination on the stimulated finger and on the heel of the hand before and after the rSS.

RESULTS

rSS improved discrimination performance, with the gain being the highest in the high-intensity group and the lowest in the low-intensity group. Measurements on the heel of the hand revealed small improvements in the high-intensity group, indicative of recruitment processes.

CONCLUSIONS

rSS of maximal intensity induced the strongest effects, indicative of a monotonic intensity-gain characteristic with no U-shaped dependency.