The Role of Cardiac Vagal Tone in Prediction of Individual Differences in Attention and Emotion Processing After Sleep Restriction
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There has been increasing interest in the mechanisms by which sleep loss impacts emotion processing. Recent investigations have begun to study physiological responses to emotional stimuli following sleep loss. There is also interest in identification of individual difference markers of vulnerability to sleep loss. The current thesis examined the effect of sleep restriction on emotional processing: subjective mood, emotion regulation style (suppression and reappraisal), behavioural response to emotional task performance, and neural responses (event-related potentials) to emotionally laden visual stimuli were examined. The role of vagal tone, indexed by Respiratory Sinus Arrhythmia (RSA), was examined as a trait-like individual difference variable for prediction of vulnerability to sleep loss. Healthy, good sleepers between the ages of 17-30 were recruited from a university population for participation in the study. The final sample of 74 participants underwent baseline ECG recording prior to random assignment to either the rested control group (C: age M = 21.03; men = 12) or sleep restriction group (SR: age M = 20.49; men = 13). All participants were well rested leading up to the experimental night when the control group had an 8 hour sleep opportunity (23:00-07:00) and the sleep restriction group had a 4 hour sleep opportunity (03:00-07:00). The day following the sleep manipulation, participants completed a number of tasks to assess the impact of sleep loss on attention and emotion. Emotional faces with varying degrees of emotional intensity were presented and were identified by expression as happy, sad, fearful, angry, or neutral; N170 event-related potentials to face stimuli were examined. Affective pictures were presented in a second task, and were identified as negative, neutral or positive by participants; the LPP event-related potential, a measure of sustained attention was examined. One night of sleep restricted to four hours was sufficient to lead to predictable impairments in alertness, mood, and reaction time. Regression analyses confirmed an effect of sleep loss on emotional processing that was moderated by RSA at baseline. RSA moderated the relationship between Group (SR, C) and LPP to positive affective pictures; low RSA was associated with altered processing of affective pictures due to sleep loss. RSA and use of suppression and reappraisal strategies for emotion regulation together moderated the relationship between Group (SR, C) and N170 amplitude to emotional face stimuli in sleep restricted participants. Overall, individual differences in RSA were predictive of performance deficits on emotion processing tasks in response to a subtle degree of sleep loss that is commonly experienced. This research has implications for daily functioning, as even a single night of restricted sleep is sufficient to impact perception and response to emotional information.