Artificial Sensations Evoked by Transcutaneous Electrical Nerve Stimulation: Investigating the Parameters Space

Transcutaneous electrical nerve stimulation (TENS) holds promise to become an effective method to restore sensations to patients with somatosensory deficits. Here we explored the parameters space of TENS to gain better understanding of the ways to generate TENS-based artificial sensations. Two experiments were conducted to investigate the relationship between TENS parameters and their evoked sensations. In the first experiment, TENS was applied passively while evoked sensations were reported by the participants. In the second experiment, an active exploration task was implemented, called “tactile vision”, where participants scanned a flat surface with a stylus to determine the shape of an invisible object. Touching an object triggered TENS. Auditory feedback was used for comparison with TENS in experiment 2. Data were collected in 11 healthy participants. In experiment 1, several TENS parameters were varied, including width, frequency, and duration. The parameters that reliably evoked somatic sensations were then used to generate sensory feedback in experiment 2. We found that electrical pulse characteristics impacted the felt intensity and naturalness of stimulation. Wider pulses resulted in more intense sensations which, however, were identified as less naturalistic. Increasing TENS duration improved familiarity. TENS feedback was adequate for the tactile vision task, but it was somewhat less effective than the auditory feedback. Overall, although TENS appears suitable for generating artificial somatic sensations, long-term training is required to improve the performance.