The following is a summary of “Decreased Default Mode Network Connectivity Following 24 Hours of Capsaicin-induced Pain Persists During Immediate Pain Relief and Facilitation,” published in the May 2023 issue of Pain by Alhajri et al.

Especially in the early phases, prolonged experimental pain models can help evaluate the cortical mechanisms underlying the transition from acute to chronic pain, such as resting-state functional connectivity (rsFC). This study examined the effects of capsaicin-induced pain for 24 hours on the default mode network rsFC, a major network in the dynamic pain connectome. At baseline, 1 hour, and 24 hours after applying a control or capsaicin patch to the right forearm, the rsFC was measured electroencephalographically in 24 healthy volunteers (12 females) using Granger causality.

The placebo patch was applied at least one week before the capsaicin patch. After 24 hours, the patch was cooled and then heated to evaluate variations in rsFC resulting from pain relief and facilitation, respectively. Compared to baseline, decreased rsFC at alpha oscillations (8-10Hz) was found following 1 hour and 24 hours of capsaicin application for connections projecting from medial prefrontal cortex (mPFC) and right angular gyrus (rAG) but not left angular gyrus (lAG) or posterior cingulate cortex (PCC): mPFC-PCC (1 hour: P<.001, 24hours: P= .002), mPFC-rAG (1 hour: P< .001, 24 hours: P= .001), rAG-mPFC (1 hour: P<.001, 24hours: P = .001), rAG-PCC (1 hour: P< .001, 24 hours: P= .004). 

At beta oscillations, rsFC decreased similarly after 1 hour and 24 hours (P≤0.008); however, projections from PCC also decreased: PCC-rAG (P≤0.005) and PCC-lAG (P≤0.006). Following 24 hours, pain NRS scores (3.7±0.4) were decreased by chilling (0.3±0.1, P =.004) and increased by heating (4.8±0.6, P=.016). Neither chilling nor heating, however, altered rsFC. This study demonstrates that 24 hours of experimental pain induces a significant reduction in DMN connectivity during pain relief or facilitation, indicating a possible transition to attentional and emotional processing in persistent pain.

Source: sciencedirect.com/science/article/pii/S1526590022004667