Study reveals sleep-wake continuum in patients with insomnia disorder

Sleep is essential for healthy functioning. Insomnia disorder is prevalent, affecting around 5 to 10% of the adult population. The primary issue is a subjective complaint of reduced quantity or quality of sleep, which is often not observed in objective sleep measurements.

Research lead by Carlotta Schneider, PhD student and assistant psychologist at UPD and UNIGE, in the research group of Prof. Christoph Nissen, Chief-physician of the Division of psychiatric specialties and Director of the Sleep medicine center (HUG), and Full Professor in the Department of psychiatry at the UNIGE Faculty of Medicine, studied sleep and serial deliberate awakenings in a sleep laboratory setting. The study involved 30 healthy participants and 30 patients with insomnia disorder.

After two nights dedicated to adaptation and sleep data collection, on a subsequent experimental night, participants in both groups were awakened up to 12 times during non-rapid eye movement (NREM) sleep via a vibrating bracelet and asked about their perception of having been asleep or awake through an automated interview.

Intact sleep-wake regulatory systems

In approximately half of the awakenings, participants in both groups reported that they had been asleep, whereas in the other half, they stated that they had been awake. High-frequency brain activity during sleep, considered an index of arousal, was associated with the perception of having been awake across groups. Although patients reported substantial subjective complaints about their sleep, objective sleep parameters and direct sleep-wake perception did not significantly differ from those of healthy participants.

The results are in line with emerging concepts of a physiological persistence of wake-like activity during sleep (sleep-wake continuum) that transcends traditional views of exclusive sleep-wake boundaries. The results also support other findings suggesting that sleep-wake regulatory systems, as assessed by current standard measures of sleep, are often intact in patients with insomnia disorder. Rather, the complaints appear to develop over time through sustained cognitive, emotional and behavioral mechanisms, which need to be further tested.

These results have potential implications for concepts of insomnia disorder and sleep-wake regulation, as well as future treatment developments. They support the notion that many patients, after exclusion of specific organic sleep or other disorders, can learn to improve their sleep-related difficulties through CBT-I, the current first-line treatment. Pharmacotherapy can be offered for short-term treatment, but can be associated with the risk of side-effects, tolerance and dependence. Further studies are currently underway on the concept of a sleep-wake continuum, potential subgroups of patients, and broader implementation of CBT-I.