Resting state EEG before and after HFS-induced central sensitization

Background and aims Animal studies have shown that high frequency electrical stimulation (HFS) of the sciatic nerve triggers longterm potentiation within spinal nociceptive circuits and long-lasting changes in thalamocortical networks, manifested as a slow-wave EEG pattern (0.5-8 Hz bandwidth), recorded from electrodes covering the parietal cortex (S1) (1). Here, we assess if HFS applied to human skin, which induces a long-lasting increase in pain sensitivity in both the area at which HFS was applied as well as the surrounding unstimulated skin, changes the ongoing EEG recorded over the left and right parietal region. Methods HFS (5 trains of 100 Hz electrical pulses lasting 1 sec each and delivered with a 10 s inter-train interval) was delivered to the left or right volar forearm of 21 healthy participants (6 males, aged 23 ± 3 years), using a multi-pin electrode designed to preferentially activate nociceptive afferents (2). Before HFS and thirty minutes after applying HFS, seventy seconds of ongoing EEG (32 channels, referenced to the mastoids) was recorded during eyes closed. The spectral content of the ongoing EEG was analyzed offline using a fast Fourier transform (FFT) on half-overlapping 2 seconds segments. Four different frequency bands were analyzed after averaging the signal from parietal electrodes C3 and C4 : delta (0–4 Hz), theta (4–8 Hz), alpha (8–12 Hz) and beta (12–30 Hz). Paired-t tests were used to test for differences in power spectrum before versus after HFS within each bandwidth. Results After HFS, a significant decrease in delta power (p = 0.046) and an increase in alpha power (p = 0.023) was observed. The power of other frequency bands was not significantly changed after HFS