How Fast Is Too Fast? Boundaries to the Perception of Electrical Stimulation of Peripheral Nerves

Area of Science:

• Neuroscience
• Biomedical Engineering
• Rehabilitation Technology

Background:

• Transcutaneous electrical stimulation (TES) offers sensory feedback for prosthetic hand users.
• Optimizing TES paradigms for event discrimination remains a challenge.
• Neural refractory periods may influence stimulus perception.

Purpose of the Study:

• To determine if the neural refractory period affects perceived stimulus amplitude in TES.
• To explore how inter-pulse interval (ipi) and inter-stimulus interval (isi) influence sensory discrimination.

Main Methods:

• A two-alternative forced choice experiment with 20 participants.
• Delivery of single or paired pulse stimuli with varying ipi (6-10 ms).
• Stimuli were presented with varying isi (250-450 ms).

Main Results:

• Paired pulses with 6 ms ipi were perceived as stronger less often than those with 8 ms or 10 ms ipi.
• Shorter isi (250 ms) reduced the likelihood of identifying paired pulses as strongest compared to longer isi (350-450 ms).
• Perceived stimulus strength did not consistently increase with higher stimulation frequencies.

Conclusions:

• Stimulation paradigms for prosthetic sensory feedback should consider neural refractory properties.
• There is an upper limit to frequency-based sensory encoding; frequencies below 125 Hz are suggested.
• Optimizing TES requires understanding the interplay between ipi, isi, and neural physiology.