Self-Referential Dysfunction and Default-Mode Hyperactivation in Psychophysiological Insomnia Patients: A Case-Control fMRI Study

Psychophysiological insomnia (PI) is one of the most frequent sleep disorders. In this study we tested whether differences in terms of neural activation are present between a group of PI patients and a healthy-control group while they are exposed to idiosyncratic ruminations and worries, evoked visually by words, so as to explore their hypothetical link with default-mode network (DMN) dysfunction in PI. We recruited five PI patients diagnosed according to the International Classification of Sleep Disorders, version 2 (ICSD-2) of American Academy of Sleep Medicine (AASM) and five age- and sex-matched healthy controls. Patients were recruited at the outpatient Sleep Medicine Centre of the Coimbra University Hospital Centre. We used a functional magnetic resonance imaging (fMRI) block-design paradigm where the participants visualized lists of words related to past/present and future concerns and also emotionally neutral words. The results suggested that the PI patients showed a failure of the DMN to deactivate. Moreover, when these patients were exposed to words concerning both past/present ruminations and future worries, there was a pronounced and significant over-recruitment of brain areas related to DMN and self-referential processing when they were compared to healthy volunteers. The differences between the patient and control groups were also evident in self-report measures. In sum, despite the relatively small sample size, our study clearly suggests that in PI there is a dysfunction in brain regions pertaining to self-referential processing, which is corroborated by an overall pattern of hyperarousal in brain regions comprising the DMN. These data may be useful in the improvement of pathophysiological models, diagnostic and therapeutic interventions for insomnia.