Pain Perception and Sleep Are Fundamental Physiologic Processes Regulated by Overlap- Ping Biologic Substrates within the Central

INTRODUCTION PAIN PERCEPTION AND SLEEP ARE FUNDAMENTAL PHYSIOLOGIC PROCESSES REGULATED BY OVERLAPPING BIOLOGIC SUBSTRATES WITHIN THE CENTRAL nervous system (CNS). Conditions associated with dysfunction of these complex systems (eg, chronic pain, insomnia, affective disturbance) are some of the most common, costly, and difficult-totreat problems facing healthcare. Longitudinal studies of chronic pain disorders indicate that exacerbations in pain are associated with disturbed sleep and that poor sleep in turn predicts increases in clinical pain.1 Although there are many possible explanations for this reciprocal relationship, one hypothesis gaining attention in animal models is that cholinergic nuclei in the brainstem, which regulate rapid eye movement (REM) sleep, may also regulate central pain-processing mechanisms.2 Several preliminary studies in humans have indeed found that sleep deprivation decreases pain threshold (eg, see references 3 & 4), but these investigations did not use laboratory measures of pain that index central pain-modulatory processes. Furthermore, because sleep loss has broad physiologic and psychological effects, sleep-deprivation studies alone do not fully elucidate the sleep-pain relationship. Uncovering a significant relationship between normal interindividual variation in sleep and individual differences in central pain processing, however, would suggest a more direct functional and neurobiologic overlap of these 2 systems. Such a relationship would also raise the possibility that sleep-related parameters could serve as modifiable risk factors for vulnerability to chronic pain. To date, no studies have reported whether individual differences in slowwave sleep (SWS) or REM sleep are associated with pain perception. The aim of this brief report is to evaluate relationships between sleep architecture and pain processing in healthy women, sleeping under normal conditions.