Slow-wave sleep and waking cognitive performance II: Findings among middle-aged adults with and without insomnia complaints.

Previous studies showing a relationship between nocturnal slow-wave sleep (SWS) and subsequent diurnal performance among young normal sleepers and older insomnia sufferers have provided limited support for the notion that this sleep stage serves a restorative role for neurocognitive functioning. The current study, which examined the relationship between SWS and reaction time performance among middle-aged adults with and without insomnia complaints, was conducted to further explore this possibility. A sample of 31 noncomplaining middle-aged (ages 40 to 59 years) normal sleepers and a like-aged sample of 27 insomnia sufferers, provided data for the current investigation. All participants underwent nocturnal sleep monitoring immediately prior to undergoing a battery of daytime tests that measured simple reaction time, vigilance/signal detection, and complex reaction time. Results showed relationships between reaction time performances on some tasks and some SWS measures among both the normal sleepers and insomnia sufferers. Findings supported our prediction that the presence of sleep pathology (e.g., insomnia) alters the SWS-performance relationship observed, but the results failed to show a consistent relationship between SWS and subsequent performance within either sample. The findings suggest that the specific performance demands of the task in question as well as physiological parameters other than SWS may determine performance as well. Findings for this and previous studies do provide some support for the contention that the neurocognitive restorative value of SWS may change across the lifespan. Possible implications of the study's findings are discussed and directions for future research are considered.