Elsevier

Neuroscience

Volume 132, Issue 2, 2005, Pages 529-535
Neuroscience

Overnight verbal memory retention correlates with the number of sleep spindles

https://doi.org/10.1016/j.neuroscience.2005.01.011Get rights and content

Abstract

Despite strong evidence supporting a role for sleep in the consolidation of newly acquired declarative memories, the contribution of specific sleep stages remains controversial. Based on electrophysiological studies in animals, synchronous sleep oscillations have been long proposed as possible origins of sleep-related memory improvement. Nevertheless, no studies to date have directly investigated the impact of sleep oscillations on overnight memory retention in humans. In the present study we provide evidence that overnight verbal memory retention is highly correlated with the number of sleep spindles detected by an automatic algorithm over left frontocentral areas. At the same time, overnight retention of newly learned faces was found to be independent of spindle activity but correlated with non-rapid-eye-movement sleep time. The data strongly support theories suggesting a link between sleep spindle activity and verbal memory consolidation.

Section snippets

Subjects

Nineteen male volunteers, paid for participation, between the ages of 26 and 54 (mean age: 37±7.6 years) participated in the study. All subjects were right-hand dominant (Edinburgh Handedness Inventory) and right-legged. To ensure relative homogeneity in learning experience during previous life stages, subjects’ education level was limited to 12 years of education. IQ (Raven) was between 95 and 134 (mean: 116.6±10.2). Participants had no prior history of neurological and psychiatric disorders,

Results

Evening verbal free recall scores (for the names) ranged between 38 and 88 points (mean: 63.3±14.8) while morning verbal free recall scores were between 36 and 100 points (only one subject achieved 100 points, mean was 67.1±18.9). Out of the 19 subjects, 12 showed positive overnight verbal retention, that is, higher verbal free recall scores in the morning compared with that in the evening. Correct morning facial recognitions ranged between 86.7 and 100% (mean: 96.1±9.5) while morning true

Discussion

The overall pattern of significant correlations suggests that both verbal and facial overnight memory retention are related to postlearning sleep; however, the underlying mechanisms within sleep are different. Overnight verbal memory retention was shown to be related to sleep spindle activity while facial memory retention seemed to depend on NREM mechanisms other than sleep spindles. Since evening memory scores did not significantly correlate with sleep measures, this also points to acute

Acknowledgments

We thank Dr. Björn Merker for helpful comments on the manuscript. This work was supported by the grant (No: 5/0079/02) of the Hungarian National Research and Development Programs.

References (22)

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