Characterizing Sensory Adaptation to Transcutaneous Electrical Nerve Stimulation: Implications for Stable Tactile Feedback in Neuroprosthetics

This study aimed to characterize peripheral nervous system adaptation to transcutaneous electrical nerve stimulation (TENS), focusing on the temporal dynamics of perceived intensity decay at different stimulation frequencies. Six healthy volunteers received constant electrical stimulation to the ring finger of the left hand in two experimental blocks at 10 Hz and 20 Hz, with current intensity individually adjusted to 80% of each participant’s pain threshold and a pulse-width of 500 μs. Perceived intensity was rated every 15 seconds over 180 seconds, and the resulting data were fitted to a piecewise exponential decay model to extract delay (d), decay amplitude (A), and time constant (τ). Median delays were 8.47 s for 10 Hz and 19.33 s for 20 Hz. No significant linear relationships were found between stimulation frequency and either delay or decay amplitude; however, a non-significant trend toward higher τ values was observed at 20 Hz (p = 0.27). Results revealed marked interindividual variability in adaptation onset and magnitude, in agreement with prior literature on both invasive and noninvasive stimulation. These findings reinforce the need for personalized and temporally dynamic stimulation protocols to maintain stable perceptual intensity in prolonged tactile feedback applications, particularly in the context of upper-limb prosthetic control.