Chronic psychophysiological insomnia: hyperarousal and/or inhibition deficits? An ERPs investigation

Abstract

Study objectives: Chronic primary insomnia has been hypothesized to result from conditioned arousal or the inability to initiate normal sleep processes. The event-related potentials (ERPs) N1, P2, and N350 are useful indexes of arousal. The objective is to compare these ERPs in primary chronic psychophysiological insomniacs (INS) and good sleepers (GS) during multiple recordings.

Participants: Participants were 15 INS (mean age = 46 years, SD = 7.5) and 16 GS (mean age = 37 years, SD = 10.1).

Methods and procedure: Following a multistep clinical evaluation, INS and GS participants underwent 4 consecutive nights of PSG recordings (N1 to N4). ERPs were recorded on the 3rd and 4th nights in the sleep laboratory (N3 and N4). ERPs recordings were made during wake on both nights (in the evening and upon awakening), with the addition of sleep-onset recordings on N4. Auditory stimuli consisted of "standard" and "deviant" tones.

Statistical analysis: Repeated measures ANOVAs were computed for each ERP for each recording for each type of stimulus.

Results: The amplitude of P2 and N350 was greater for the deviant than for the standard stimulus in both groups. The amplitude of N1 was larger in INS than GS in the morning and the evening. While the amplitude of N350 was larger in GS than in INS at sleep onset, the amplitude of P2 was greater in INS than in GS at that time.

Conclusion: Signs of greater cortical arousal in psychophysiological insomnia individuals are observed, especially upon awakening in the morning. However, at sleep onset, difficulties from disengaging from wake processes and some inability at initiating normal sleep processes appear also present in individuals with insomnia compared to good sleepers.

Figures

Figure 1

ERPs results for good sleepers and psychophysiological insomnia sufferers during morning recordings. GS = Good sleepers; INS = psychophysiological insomnia sufferers; M3 = third morning of PSG recordings and first morning of ERPs recordings; M4 = fourth morning of PSG recordings and second morning of ERPs recordings. Significant between groups difference is illustrated with the black circle.

Figure 2

ERPs results for good sleepers and psychophysiological insomnia sufferers during evening recordings. GS = Good sleepers; INS = psychophysiological insomnia sufferers; E3 = third evening of PSG recordings and first evening of ERPs recordings; E4 = fourth evening of PSG recordings and second evening of ERPs recordings.

Figure 3

ERPs results for good sleepers and psychophysiological insomnia sufferers during sleep-onset recordings. GS = Good sleepers; INS = psychophysiological insomnia sufferers; SO = sleep-onset recordings taking place on the fourth evening of PSG recordings. Between groups significant differences are illustrated with the black circles.