A Possible Occurrence of Delta Rebound During Neurofeedback Training ―Clinical Implications From a Case Report ―

Abstract: Neurofeedback (NF) has been increasingly applied to post-traumatic stress disorder (PTSD); however, the neurophysiological mechanisms underlying its clinical effects remain incompletely understood. This case report describes EEG spectral changes observed during an 11-week course of NF training in a male patient in his 50s diagnosed with PTSD. A low-beta NF protocol was applied (15–18 Hz reward; 2–8 Hz and 22–36 Hz inhibition), and resting-state EEG was recorded during eyesopen resting state and eyes-closed resting state. Spectral analysis was performed using the maximum entropy method (MEM). Following the sixth NF session, a marked but transient increase in delta band power (1–4 Hz) was observed during the eyes-open resting state; this increase subsequently subsided and returned to baseline levels, suggesting a rebound phenomenon rather than a sustained training effect. In contrast, alpha band power (8–12 Hz) during the eyes-closed resting state showed a sustained increase over the course of training. Subjectively, a temporary worsening of symptoms coincided with the delta increase, followed by persistent improvements in sleep stability, disappearance of traumarelated dreams, and enhanced emotional regulation, which were corroborated by clinical evaluation. The transient delta increase was interpreted as a possible delta rebound phenomenon reflecting a transitional phase of NF-induced neural reorganization rather than drowsiness or protocol failure. Although limited to a single case, these findings suggest that NF effects in PTSD may involve dynamic, multi-band EEG adjustments at the network level, warranting further systematic investigation. Keywords: EEG, Neurofeedback, Delta rebound, Low-beta training, PTSD,