Exploring the relationship between meaningful conditioned pain modulation and stress system reactivity in healthy...

The sympathetic nervous system (SNS) and hypothalamic-pituitary-adrenal (HPA) axis have been implicated in conditioned pain modulation (CPM). As there has recently been a push to identify meaningful CPM responses based on ± 2 SEM of the test stimulus, we sought to evaluate if meaningful CPM had relationships with both SNS and HPA axis reactivity.

50 university-aged healthy participants (25 males, 25 females) underwent evaluation of pressure pain detection threshold (PPDT), conditioned pain modulation (CPM), galvanic skin response (GSR) and salivary cortisol before and after a cold pressor test (CPT). Meaningful CPM was evaluated based on change ±2 SEM of baseline PPDT to classify participants as experiencing inhibition of pain, facilitation, or non-response.

As a group, there were no significant changes in PPDT or salivary cortisol after exposure to noxious cold. GSR was significantly elevated from baseline values during the CPT, and 10 min after (p < 0.001). When meaningful CPM was assessed, only 30% of participants experienced inhibitory CPM. Within this group, there was a large positive correlation ranging from r = 0.63 to 0.69 (p < 0.01) between CPM and the absolute change in GSR from baseline to immersion, and the immediate 5 min after immersion.

This work continues to support the growing body of literature suggesting that CPM is not universally experienced. Inhibitory CPM may be associated with an increase in SNS activity for healthy participants in reaction to noxious cold. Future work is required to ascertain individual characteristics (e.g., age, sex) that relate to CPM responses.