Introduction Existing data demonstrate reduced delta power during sleep in chronic pain and depressed patients. However, there has been little examination of the relationship between delta power and next-day reports of pain. We tested the extent to which nocturnal (during the concurrent sleep period) and daytime pain reports are associated with delta power during sleep, as well as the extent to which this association is moderated by depressive symptoms. We hypothesised that reduced delta power and SWS would be associated with increased pain, pain catastrophising, and pain sensitivity.

Methods 149 female participants with insomnia and temporomandibular joint pain (TMD) were recruited. We examined nocturnal and daytime measures of pain (pain severity, average pain), pain catastrophizing, and objective pain sensitivity (obtained through quantitative sensory testing (QST)), and calculated relative nocturnal delta (0.5-3.4 Hz) power using polysomnography. We fit linear regression models correcting for depressive symptom severity, age, and total sleep time, and further examined the moderating effect of depression severity on these measures.

Results reduced delta power was associated with increased average nocturnal pain (Unstandardized β = -17.67, p= 0.02), morning pain (Unstandardized β = -15.67, p=0.02), and average next-day pain (Unstandardized β = -16.74, p= 0.03). Depression severity did not moderate these relationships. Delta power was not significantly associated with objective pain-sensitivity, nocturnal, or daytime pain catastrophising. However the association between nocturnal pain catastrophising and delta power was moderated by depressive symptom severity (p = 0.04). Simple slopes analysis revealed that when participants had low depressive symptoms (<13 CESD), increased delta power significantly predicted reduced nocturnal pain catastrophising.

Discussion These findings demonstrate that delta power during sleep is associated with both nocturnal and daytime experience of pain in patients with TMD. In patients with TMD and low depressive symptoms, reduced delta power was associated with increased nocturnal pain catastrophising.