ERP evidence of enhanced excitatory and reduced inhibitory processes of auditory stimuli during sleep in patients with primary insomnia

Study Objectives: Increased information processing around the onset of sleep and during sleep has been suggested as an important factor for the pathogenesis of insomnia. The purpose of the present study was to examine the processing of auditory information during sleep in patients with insomnia through the recording of event-related potentials (ERPs). Design: A mixed design was used in which subject group was a betweensubject factor and sleep stage and type of tone presented were withinsubject factors. Participants: Fifteen patients with primary insomnia and 15 normal sleepers (controls) were studied. Measurements and Results: An odd-ball paradigm was conducted to evoke ERPs throughout the night. Patients with insomnia showed larger N1 and smaller P2 to rare tones, smaller N350 to standard tones, and slower P900 to both tones during the first 5 minutes of continuous stage 2 sleep. No consistent ERP differences were detected between the 2 groups when the waveforms were averaged across the whole night. Conclusions: Patients with insomnia showed an enhancement in attention and a reduction in the inhibitory process that normally facilitates sleep onset in the beginning part of sleep. The results partially support the hyperarousal theory, ie, enhanced information processing during the initiation of sleep is a contributing factor for insomnia.