Psychomotor performance deficits and their relation to prior nights' sleep among individuals with primary insomnia.

PRIMARY INSOMNIA (PI) IS A PREVALENT AND SERIOUS HEALTH CONCERN CHARACTERIZED BY COMPLAINTS OF CHRONIC NOCTURNAL SLEEP disturbance and associated daytime impairment occurring in the absence of any contributory medical or psychiatric condition. Current evidence suggests that 1% to 2%1,2 of the general population and approximately 20%3,4 of patients encountered in clinical settings suffer for this form of sleep difficulty. Since PI persists in the absence of medical/psychiatric causes, there is, perhaps, a temptation to minimize the seriousness of this condition. However, epidemiologic studies show PI substantially increases health care utilization/costs and absenteeism from work among affected individuals.3,5,6 Also, numerous studies have shown that PI dramatically increases risks for depressive illness even after other significant predictors are statistically controlled.7–9 In addition, PI contributes to reduced productivity, work-related accidents, increased alcohol consumption, serious falls among the elderly, and a general sense of being in poor health.10–14 Anecdotal observations suggest that PI sufferers are well aware of their day-to-day impairment. Indeed, clinical observations suggest such patients commonly view themselves as sleepy, fatigued, cognitively impaired, and generally not as “mentally sharp” as they recall themselves to be prior to the onset of their sleep difficulties. Despite such common reports, laboratory-based studies conducted with PI sufferers have shown that the daytime deficits of such individuals are rather elusive and difficult to document phenomena. In fact, in a recent summary prepared for the 2005 NIH State-of-the-Science Conference on the Manifestations and Management of Chronic Insomnia in Adults, Bonnet15 noted that studies of daytime psychomotor deficits among PI sufferers have produced significant findings at no better than chance levels. Given such mixed findings, some researchers have attributed PI sufferers' diurnal complaints to such traits as their dysfunctional beliefs about the impact of insomnia on functioning16 or excessive self-focus17 rather than to any “real” or measurable daytime impairment. Evidence17–20 suggests these traits are indeed pronounced among PI sufferers, yet it is not clear that such individuals are devoid of diurnal psychomotor deficits. A review of the previous investigations of PI sufferers' performance deficits shows these studies generally included small and/or poorly characterized samples or employed a limited range of psychomotor performance measures. As a consequence, methodological limitations (e.g., limited statistical power, mixed insomnia samples, insensitive psychomotor tests) may, at least in part, explain the mixed results in this literature. Given the above-noted long-term morbidity associated with PI, it seems likely that individuals with this condition should show measurable day-to-day impairments as well. Thus, the current study was conducted to compare the diurnal psychomotor performances of well-characterized PI sufferers and non-complaining normal sleepers in a large study sample tested with a range of simple and complex psychomotor reaction time tasks. We predicted that our PI sufferers would perform significantly worse than the normal sleepers on performance measures, and group differences would be most obvious on more complex tasks. In addition to testing this hypothesis, we examined the association between the observed daytime performance deficits and both subjective and objective sleep measures derived from nights preceding our daytime testing.