Research indicates that habitual short sleepers show more rapid
accumulation of slow-wave sleep at the beginning of the night. Enhancement in
performance on declarative memory tasks has been associated with early NonREM
sleep, consisting of the highest percentage of slow-wave sleep. Twenty-four
subjects (8 short sleepers ≤7 hrs, 9 average >7 but <9 hrs, 7 long
≥9hrs) were tested. Subjects were presented with unfamiliar face stimuli
and asked to memorize them for a subsequent test. Following sleep, the subjects
were presented with the 40 “old/studied” items intermixed with
40 new and asked to indicate the previously presented stimuli. Event-related
potentials (ERPs) were analyzed to verify the existence of the
“Old/New” effect, i.e. amplitude difference [in
ERPs] between the old and new stimuli. ANOVA on the scores revealed a
significant interaction between the stimuli and group. Post-hoc test on the
studied items revealed more accurate responses in the short sleepers compared to
the average and long sleepers. Strikingly, the long sleepers, failed to show
significant retention of the old/studied items, with their recognition of old
faces not different from chance. RT responses were faster for the old versus the
new items. Pearson correlation revealed a significant negative correlation
between accuracy and sleep duration in the short sleepers. However, long and
average sleepers showed a positive correlation between the two variables. ANOVA
performed on the ERPs revealed main effects of stimuli and site, and no
interactions involving the group factor. In conclusion, our data show that
individual differences in recognition memory performance may be associated with
differences in habitual sleep duration.