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Abstract:
Abstract: Evidence exists for time-of-day effects on tasks
that assess frontal lobe capacities, yet data are sparse concerning
effects on other measures of cognition. Further, often potentially
important information is lost by separating time-of-day, a
naturally continuos variable, into discrete "morning" and
"afternoon" epochs. We examined the performance of 82 older normal
subjects (mean age 69.4) on tests of executive functions, working
memory, reaction time, and short-term memory. All analyses treated
time of day as a continuous variable and covaried for age and years
of education. We documented eating and sleeping patterns by having
all participants observed in the MIT Clinical Research Center
throughout the day. The results showed significant (p < .05)
or marginally significant (p< .10) bell-shaped quadratic time-of
day effects for measures of short-term memory and executive
functioning. Storage task performance peaked at midday, whereas
working memory tasks showed a significant linear decline as the day
progressed. Reaction time tests seemed to show a "siesta effect,"
with poorer performance after lunch than before. Overall,
time-of-day had differential effects on a spectrum of cognitive
tasks.
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