Insomnia and related sleep complaints are highly prevalent among older adults, leading to mood and cognitive problems and a reduced overall quality of life. Sleep problems are difficult to assess and understand, however. A diagnosis of insomnia depends on both subjective and objective criteria—a perceived experience of sleep deprivation and an objective duration of unwanted sleeplessness.
The difference between the subjective and objective duration of sleep is referred to as sleep discrepancy. Some individuals report high degrees of sleep difficulty but do not meet the objective clinical criteria for insomnia (which includes 30 or more minutes of inability to sleep), while others who meet the objective criteria for insomnia do not report any subjective sleep complaints. A study in the Journals of Gerontology examines the relationship between sleep discrepancy and insomnia, identifying potential clinically useful factors associated with sleep discrepancy.
The authors suggest that sleep discrepancy is best understood not as an error on the part of individuals with sleep complaints, but as a clinically useful indicator of related sleep, mood, or health concerns. To examine the significance of sleep discrepancy, the researchers assessed whether or not individuals with sleep complaints had higher rates of sleep discrepancy than those without sleep complaints, among individuals both with and without the objective criteria of insomnia.
The analysis was based on 142 participants, age 60 or better, who provided two weeks of objective and subjective sleep data. Participants were asked to wear an actigraph, a wristband that measured their movement before and during sleep (serving as a proxy measure of objective sleep), and to maintain a sleep diary in which they would report their perceptions of sleep quality during the previous night upon waking. The researchers looked at two periods of sleep difficulty: the first attempt to sleep at night (referred to as SOL, or sleep onset latency), and any unplanned time awake during the night (wake after sleep onset, or WASO). Participants were also administered the Beck Depression Inventory (a measure of depressive symptoms), a cognitive test, and an overall health survey. For the analysis, the researchers looked at whether individuals who complained of sleep problems at the beginning of the study period had a greater sleep discrepancy than those without sleep complaints.
When controlling for associated demographic and medical variables, individuals who experienced both subjective and objective criteria for insomnia had greater amounts of WASO sleep discrepancy than participants who did not report sleep complaints and/or did not meet objective criteria for insomnia. Sleep discrepancy at both SOL and WASO was associated with higher levels of depressive symptoms.
Based on their findings and on existing neurological sleep research, the authors suggest that sleep discrepancy may be associated with localized sleep disturbance, in which localized brain networks may not achieve a normal resting state while the individual is asleep. The authors argue that more research is needed on the relationship between sleep perception, physical sleep, and mood.
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