Psychophysiological responses to auditory stimuli during sleep in posttraumatic stress disorder

Abstract

Sleep complaints are common in people who develop Post Traumatic Stress Disorder (PTSD). PTSD-related information processing abnormalities evident during wakefulness might continue into sleep. A group of Vietnam veterans with and without PTSD (patients and combat-controls) were studied to examine psychophysiological responses to auditory stimuli during stage 2 NREM sleep. Three stimuli (500 ms) categories were presented in an oddball paradigm: pure tones (standard, 60% probability of occurring); trauma-related (i.e., combat sounds) and affectively neutral, environmental stimuli (20% each). The effects of stimulus presentation on evoked K-complexes, heart rate (HR), and cortical activity (power spectra ratio of fast to slow EEG activity, and beta-band power) were examined; the impact of evoking a K-complex (KC+ and KC- trials) on these last two measures was also examined. Significantly fewer K-complexes were elicited in patients; there were no within group differences in the proportion of K-complexes elicited between tone and trauma stimuli. Patients unexpectedly produced significantly more K-complexes to neutral stimuli. Examination of the N550 component of the evoked K-complex revealed significantly longer latencies in the control group, who also had longer latency for trauma stimuli relative to tone and neutral stimuli. There were no findings on N550 amplitude. Cortical arousal results ran contrary to predictions. Rather, controls demonstrated modest increases in overall cortical activity post-stimulus, while patients demonstrated decreases that were even more pronounced for KC+ trials. Beta activity was marginally higher in controls, and for KC+ trials for both groups. The smallest beta power increase was to trauma stimuli for both groups; in controls, beta activity increased most to neutral stimuli. Tonic heart rate was found to be (marginally) elevated in patients. There was no impact on initial HR decelerations, but analysis of the ensuing HR acceleration revealed a main effect of K-complex type (greater HR increases for K+ trials) and stimulus type (significantly higher increases to neutral stimuli), Results suggest sleep-related information processing is altered in PTSD and conflicting evidence for cortical and autonomic hyperarousal during sleep in PTSD, although further research is necessary to establish the generalizability to other populations (such as acute PTSD or other anxiety disorders).