Electroencephalographic power ratio and peak frequency difference associate with central sensitization in chronic pain

<i>Objective.</i>Central sensitization, or increased responsiveness of the central nervous system to sensory input, is present in many chronic pain patients. Clinically, it is detected through subjective, patient-reported measures. There is a need for reliable, direct measurements of neural response to controlled stimuli to quantify neuronal dysfunction in pain. The goal of this work is to investigate cortical activity, recorded via electroencephalogram (EEG), during objective and calibrated painful stimulation in chronic pain patients.<i>Approach.</i>Chronic pain patients (<i>N</i>= 8) and healthy controls (<i>N</i>= 8) participated in this study. We recorded electroencephalography (EEG) at rest (baseline) and during evoked pain tasks, including thermal and mechanical stimuli. The evoked pain was applied following the quantitative sensory testing (QST) protocol, which is a research technique that applies objective, calibrated painful stimuli.<i>Main results.</i>Peak alpha frequency at rest was significantly lower in chronic pain patients compared to healthy controls (<i>p</i>< 0.0002), while EEG alpha/theta and alpha/beta power ratios at rest were higher in patients (<i>p</i>< 0.0002). During thermal QST, these power ratios decreased in patients and increased in controls (<i>p</i>< 0.0002 for both). During mechanical QST, power ratios decreased or did not change. Furthermore, the peak theta-beta frequency difference at baseline was significantly lower in patients compared to controls (<i>p</i>< 0.0002). During thermal QST, this difference increased in patients and decreased in controls; during mechanical QST, this difference increased in both patients and controls (<i>p</i>< 0.0002). Functional connectivity analysis showed that controls had greater baseline theta connectivity strength that increased during mechanical QST (<i>p</i>< 0.0002).<i>Significance.</i>This work demonstrates differential patterns of EEG activity at rest and during acute painful stimulation in chronic pain patients compared to healthy controls. These measures may quantify an individual's tendency to experience chronic pain and central sensitization and serve as diagnostic biomarkers.