MSLT-defined sleepiness and neuropsychological test performance do not correlate in the elderly

This study investigated whether a sensitive, physiological measure of alertness/sleepiness, the Multiple Sleep Latency Test (MSLT), was related to neuropsychological test performance in elderly individuals. We hypothesized that the greater likelihood of falling asleep during the daytime on the MSLT would be related to relatively poorer performances on a variety of neuropsychological tests. Results from a homogeneous sample of 35 relatively well-educated, high functioning, elderly community volunteers confirmed the presence of characteristic levels of daytime alertness which were stable within individuals (r = .70 to .73) and showed large variation across individuals (coefficients of variation: 54-84%). Despite this wide intersubject variability, MSLT-defined alertness/sleepiness was unrelated to neuropsychological test results. We discuss these results in terms of the performance deficits known to accompany sleepiness in experimental studies of sleep deprivation and in terms of the behavioral slowing known to occur in normal aging.