Beta Electroencephalographic Oscillation Is a Potential GABAergic Biomarker of Chronic Peripheral Neuropathic Pain

FIGURE 1. Resting-state EEG recording protocol (A). This 24-min experiment started with a 2-min period, during which the participant opened his eyes (yellow color), and for the rest of the experiment, the eyes had to remain closed (green color). Four acoustic cues (“beeps,” vertical arrows) were presented to the participant during the experimental session to warn him about the ongoing experimental step, i.e., to switch to the eye-closed condition or to keep him awake. Each participant was instructed concerning the meaning of each acoustic cue before the beginning of the experiment. First and last beeps (t_0 and t_3, respectively) determined the beginning and the end of the experimental session, respectively. Second beep (t_1) occurred 2 min after t_0 and instructed the participant to close his eyes, whereas the third beep (t_2) occurred in the middle of the experiment and was implemented to maintain the participants awake as they tend to fall asleep. Alpha GPS-derived topoplots in all chronic neuropathic pain patients during eye-closed (B) and eye-open (C) experimental steps. The color bar at the right side of the figures represents ascending alpha power values from the lowest at the…

FIGURE 2. Power spectral densities averaged over all selected epochs in one chronic neuropathic pain patient (A) and in one control (B). In both graphs, power spectral densities obtained in the eye-closed condition, after selection of epochs recorded in wakefulness and 2 s-windowed-Fourier transform between 2 and 48 Hz (see section “Materials and Methods”), were plotted against the whole analyzed frequency spectrum. Each trace represents one channel (i.e., one electrode). One prominent peak is observed as expected, in the α range (8–12 Hz) (cf. eye-closed condition). Two additional peaks were seen within the low β (Lβ; 13–20 Hz, light red color) and high β (Hβ; 20–30 Hz, light green color) sub-bands, both in patients (A) and in controls (B). No peak was observed in the delta (δ; 2–4 Hz, light gray) frequency range. β peaks occurred, respectively, approximately 16 and 25 Hz in most participants, as illustrated by the two vertical black arrows in the two insets showing the GPS computed over all frequencies derived from each main graph, respectively. GPS in the low β (Lβ), high β (Hβ), and δ frequency ranges for chronic neuropathic pain patients and healthy controls. All data are shown as…