Restorative Sleep (Part 2)
Colin Shapiro, MD, PhD
University of Toronto
A forthcoming children's book describes the function of sleep and settles firmly on the notion that the restorative role of sleep is the most parsimonious. This is based on a lay concept onto which a wall of scientific evidence was built in the 70's and 80's with reviews of the marshalled evidence (eg Shapiro 1982). Although even children and their parents make clear statements of wanting restorative sleep, the professionals do not have a consensus of what this may be and how it is too be measured. Clearly their needs to be a multimodal approach with both subjective and objective facets. In the former there are many components that a priori may be expected to contribute to a "restorative feeling". These would include Growth hormone release; the ratio of stage 4 of stage 3 sleep; sleep efficiency and sleep fragmentation. In the subjective domain a complex series of consideration would include : Alexothymia ; response style ; personality dimensions eg hysteria; mood; cognitive and physical dimensions.
The time is now (the Walrus said) to make restorative sleep a priority.
Edward O Bixler, PhD
Pennsylvania State University
Hershey, PA, USA
Data from the Penn State Cohort, a representative sample of the general public in Central Pennsylvania consisting of 1,741 men and women across a wide age range. The association between the subjective complaints of insomnia including non-restorative sleep and the objective assessment of sleep patterns based on polysomnography are examined.
Andrew Krystal, MD, MS
Duke University Medical Center
Non-restorative sleep is one of the 3 types of sleep difficulties that currently define insomnia.
Individuals complaining of difficulties falling asleep and staying asleep have been the subject of many studies. In contrast, relatively little research has been carried out in individuals who report non-restorative sleep, despite the fact that such people are not rare. One factor limiting research in this area is that there has not been a recognized objective correlate of patients' reports of the degree of restoration they experience from their sleep that could be employed. The population of patients in which non-restorative sleep tends to be most frequently reported are those with chronic pain, fibromyalgia, and chronic fatigue syndromes. In these individuals there have been some studies suggesting increased alpha frequency EEG activity in non-REM sleep. However, these observations have not led to the development of a physiologic correlate of sleep restoration.
One consideration is that such patients also have disturbances evident in traditional sleep measures (e.g., arousals, awakenings, WASO). As a result the degree to which an increase in alpha activity is specifically related to the experience of restoration remains unclear. Further, no studies have been carried out directly examining the correlation of non-REM EEG alpha power and the reported degree of restoration with sleep. Also, because complaints of non-restorative sleep are not restricted to individuals with these types of difficulties, it is important to determine if non-REM EEG alpha power relates to non-restoration in other populations of insomnia patients. In order to directly assess the relative relationships of traditional PSG measures of sleep vs. non-REM EEG frequency content with ratings of sleep restoration, we carried out a pilot study in 30 individuals with primary insomnia. We compared the correlation of restedness ratings derived from sleep logs with both traditional PSG measures and non-REM EEG spectral power indices.
We found that ratings of restedness were significantly correlated with a relatively lower non-REM EEG power in the sigma frequency band. As a result, this measure merits further study as a possible physiologic correlate of the degree of restoration experienced with sleep in patients with insomnia.