Facial EMG responses to emotional stimuli related and nonrelated to sleep in people with primary insomnia and in good sleepers

The role of emotional arousal in insomnia is theoretically considered as a predisposing and a perpetuating factor (e.g. Morin, 1993) but, so far, no study has evaluated it directly. The aim of this study was to compare physiological and subjective responses of a group of young people with chronic primary insomnia and of a control group to emotional stimuli related or not related to sleep. Twenty-one people with insomnia and eighteen good sleepers took part to the study. Participants were invited to watch and rate a set of neutral, positive and negative pictures taken from the International Affective Picture System (IAPS, Lang, Bradley, Cuthbert, 2001) and a set of previously validated pictures related to ‘good sleep’ and ‘poor sleep’. Physiological measures included the recording of facial activity over the corrugator and the zygomatic muscles. Subjective ratings were measured through the Self-Assessment Manikin (SAM, Bradley, Lang, 1994). Preliminary results on 25 participants (12 people with insomnia and 13 good sleepers) indicated that people with insomnia present higher activity in the zygomatic muscle in response to all stimuli. Positive and sleep-positive stimuli elicited a higher response in both the groups in the zygomatic muscle compared to the negative and the sleep negative stimuli. No significant effect was found respect to the corrugator muscle. Respect to the subjective ratings, people with insomnia rated all stimuli as more arousing compared to good sleepers. Moreover, only people with insomnia rated as emotionally activating the stimuli associated with poor sleep, but not those related to good sleep. Results are consistent with Lundh and Broman’s theory of insomnia (2000), which suggests that primary insomnia is characterised by a predisposition in responding with high levels of arousal to new, sudden or emotional stimuli (hyperarousability).