0798 MEMORY FOR NOCTURNAL AWAKENINGS: TIME COURSE AND AUTONOMIC AROUSAL

Abstract

Memory is weaker for stimuli presented closer to sleep onset. Cortical arousal, which is greater in people with insomnia, is associated with less of this amnesia. This lower amnesia has in turn been suggested to explain sleep misperception in insomnia. Previous research has examined memory immediately prior to sleep onset and the influence of cortical arousal, primarily using daytime nap paradigms. The goal of this study was to explore the time course of memory across an awakening from nocturnal sleep and the influence of autonomic arousal. Forty healthy participants (mean age 20.28, SD=2.31; 65% female) completed one night of polysomnography. After five minutes of continuous N2 sleep in the third NREM period, participants were woken, kept awake for 15 minutes, and then allowed to return to sleep. Throughout this period of wakefulness, auditory word stimuli were presented every 30 seconds. In the morning, participants completed recognition testing. Stimuli were divided by which third of the awakening they were presented and recognition was compared. Greater autonomic arousal was operationalized as lower parasympathetic control of cardiac rate (respiratory sinus arrhythmia; RSA), derived from electrocardiogram. There was a significant difference in recognition of stimuli by which third of the awakening they were presented, F(2, 117)= 30.25, p<.0001. Recognition for the first third (M=62%, SD=18%) was greater than the middle third (M=44% SD=21%), which in turn was greater than the final third (M=31%, SD=14%), Bonferroni-corrected post-hoc comparison p’s<.01. Recognition of stimuli presented during the final third was negatively correlated with RSA, r(40) = -.32, p<.05. Recognition of stimuli presented during the first and middle thirds were not associated with RSA, p’s>.4. Memory was strongest for stimuli presented in the first third of an awakening from sleep and weakest for stimuli presented in the final third, closest to sleep onset. This suggests that the effect of primacy, but not recency, holds for stimuli presented during awakenings from sleep. Lower autonomic arousal was associated with weaker memory, but only for stimuli presented during the final third of the awakening when recognition was lowest. University of Arizona GPSC grant RSRCH-512 FY’15.