Participant characteristics.

Background
Due to the complexity of pain, involving physical, psychological, emotional and social aspects, we are still unable to objectively quantify or fully understand this subjective experience. An increasing number of studies have attempted to identify biomarkers of pain using brain imaging tools like magnetoencephalography (MEG). In this study, we used machine learning to investigate the potential of MEG data as a biomarker for chronic pain and used this biomarker to quantify spinal cord stimulation (SCS) treatment effect.
Methods
The study population consisted of 25 patients with SCS, for whom we recorded resting-state MEG during tonic, burst and sham stimulation, 25 patients with chronic pain and 25 pain-free controls. We derived average power spectral densities across each of the 94 automated anatomical labeling atlas based brain regions and extracted six spectral features: the alpha peak frequency, alpha power ratio, and average power across the theta, alpha, beta, and low-gamma bands. Based on these features, we used automated machine learning to find the optimal combination of machine learning methods to create classification and regression models for pain and pain intensity.
Results
The theta power and alpha power ratio were the most promising features to classify chronic pain with an accuracy of 76%. The classification model outputs and self-reported pain scores of patients with SCS showed a Spearman correlation coefficient of 0.12. A regression model based on pain scores of all participants showed Spearman correlation coefficients between 0.27 and 0.41.
Conclusion
This study achieved a promising 76% accuracy in classifying patients with chronic pain and pain-free controls using the theta power or alpha power ratio. However, this model’s output poorly correlated with pain scores of patients with SCS. A larger variety of input features and outcome parameters is recommended.