The stability of perception threshold tracking for long session evaluation of Aβ- and Aδ-fiber function

Research has proven that epidermal and transcutaneous stimulation can identify the function of Aβ and Aδ fibers (i.e., in diabetes) individually using different electrodes. In this study we aimed to determine the stability of perception thresholds when using such electrodes.

Twenty healthy volunteers participated in this study. The perception threshold of Aβ fibers (patch electrode) and Aδ fibers (pin electrode) was estimated 30 times during a period of 60 minutes. A threshold was established every other minute, alternating between the two electrodes. The stimulus duration was 1 millisecond and the interstimulus interval was 1.5 to 2.5 seconds. Linear regressions of the perception threshold as a function of time were performed. The slopes were used as an estimate of habituation and were compared between the electrodes.

The slope was significantly larger when assessed by the pin electrode (median: 0.020 [0.009 to 0.030] mA/trial) than when assessed by the patch electrode (median: 0.005 [0.001 to 0.018] mA/trial) (P = .017, paired t test). During the session, total increases in perception threshold of approximately 55% and 1% were seen for the pin and patch electrodes, respectively.

The two fiber types assessed showed significant perception threshold increases. The higher slope of the pin electrode indicated that the Aδ fibers were more prone to habituation than the Aβ fibers, and that habituation should be considered during prolonged experiments. This assessment is valuable for future research on nerve fiber function using the technique for long session experiments.