Effects of stimulation frequency and pulse width in transcutaneous auricular vagus nerve stimulation on finger somatosensory function.

Transcutaneous auricular vagus nerve stimulation (taVNS) is a noninvasive electrical stimulation technique applied to the left cymba concha that may improve somatosensory impairment in stroke. Although previous studies have investigated various stimulation parameters, the optimal stimulation parameters for somatosensory impairment remain unknown. Therefore, the aim of this study was to determine the effective taVNS stimulation frequencies and pulse widths that enhance somatosensory function in the fingers. Experiments 1 and 2 each included 30 healthy, right-handed university students. In Experiment 1, the taVNS stimulation frequency was set to 30, 25, and 20 Hz, with a pulse width of 100 µs. In Experiment 2, the taVNS stimulation frequency was set to 25 Hz, with pulse widths of 300 µs and 500 µs. In Experiments 1 and 2, 2PD measurements were taken before taVNS, immediately after stimulation, and 20 min after stimulation ended. The results showed that Experiments 1, stimulation frequencies of 30 Hz, 25 Hz, and 20 Hz did not produce significant changes in 2PD thresholds. In contrast, Experiments 2, taVNS delivered at 25 Hz with pulse widths of 300 µs or 500 µs significantly reduced 2PD thresholds immediately after stimulation and again 20 min later.