Identifying EEG biomarkers of fatigue and brain fog in long COVID: insights from rest and movement-related brain activity.

BACKGROUND: Fatigue and brain fog are among the most reported symptoms in Long COVID (LC), yet their underlying neural mechanisms remain unclear. In this context, we aimed to identify neural correlates associated with LC symptoms. METHODS: Electroencephalography (EEG) was used to quantify brain oscillatory activity during sustained handgrips and rest in the left central region overlying the primary hand motor (C3) and somatosensory areas (C5). A sample of twenty LC participants reporting fatigue, brain fog, and post-exertional malaise (PEM) was analyzed, along with 20 age- and sex-matched controls. All participants were right-handed, and EEG activity was recorded on the dominant left hemisphere over motor and somatosensory areas. The main LC symptoms were assessed using the Fatigue Severity Scale (FSS), the Cognitive Failures Questionnaire (CFQ), and the DePaul Symptom Questionnaire for PEM (DSQ-PEM). RESULTS: LC participants showed a smaller post-movement beta rebound (PMBR) during handgrips in the left central region (electrode C3, p = 0.02) compared to controls, which negatively correlated with cognitive symptoms (r = -0.35, p = 0.02). They also showed a slower alpha central frequency (CF) at rest (electrode C5, p = 0.003), which correlated with fatigue (r = -0.264, p = 0.019). CONCLUSIONS: Both the lower PMBR and slower alpha CF suggest impaired inhibitory control and reduced excitability in the sensorimotor cortex of LC individuals. Together, these features, which were associated with fatigue and brain fog, highlight altered dynamics in the sensorimotor cortex of LC individuals. These findings offer preliminary mechanistic insight into LC symptoms and suggest that PMBR and alpha CF warrant further investigation as candidate EEG markers of this condition.