Brain oscillations reflecting pain-related behavior in freely moving rats

Recording oscillatory brain activity holds great promise in pain research. However, experimental results are variable and often difficult to reconcile. Some of these inconsistencies arise from the use of hypothesis-driven analysis approaches that do not assess the consistency of the observed responses within- and across-individuals, and do not fully exploit information sampled across the entire cortex. Here we address these issues by recording the electrocorticogram directly from the brain surface of 12 freely-moving rats. Using a hypothesis-free approach we isolated brain oscillations induced by graded nociceptive stimuli, and characterized their relation to pain-related behavior. We isolated four responses, one phase-locked event-related potential, two non-phase-locked event-related synchronizations (ERS), and one non-phase-locked desynchronization (ERD), in different frequency bands (δ/θ-ERD, θ/α-ERS, γ-ERS). All responses except the δ/θ-ERD correlated with pain-related behavior at within-subject level. Notably, the γ-ERS was the only response that reliably correlated with pain-related behavior between subjects. These results comprehensively characterize the physiological properties of the brain oscillations elicited by nociceptive stimuli in freely-moving rodents, and provide a foundational work to improve the translation of experimental animal findings to human physiology and pathophysiology.This is an open access article distributed under the Creative Commons Attribution License 4.0 (CCBY), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.