Consolidation of Associative Memory

Hippocampal sharp wave/ripples during sleep for consolidation of associative memory.
Ramadan W, Eschenko O, Sara SJ.
PLoS One. 2009 Aug 20;4(8):e6697.

The beneficial effect of sleep on memory has been well-established by extensive research on humans, but the neurophysiological mechanisms remain a matter of speculation. This study addresses the hypothesis that the fast oscillations known as ripples recorded in the CA1 region of the hippocampus during slow wave sleep (SWS) may provide a physiological substrate for long term memory consolidation. We trained rats in a spatial discrimination task to retrieve palatable reward in three fixed locations. Hippocampal local field potentials and cortical EEG were recorded for 2 h after each daily training session. There was an increase in ripple density during SWS after early training sessions, in both trained rats and in rats randomly rewarded for exploring the maze. In rats learning the place -reward association, there was a striking further significant increase in ripple density correlated with subsequent improvements in behavioral performance as the rat learned the spatial discrimination aspect of the task. The results corroborate others showing an experience-dependent increase in ripple activity and associated ensemble replay after exploratory activity, but in addition, for the first time, reveal a clear further increase in ripple activity related to associative learning based on spatial discrimination.

Secrets of the Sleeping Brain

Why do we sleep? Although science has yet to explain the reason we spend one-third of our lives in this bizarre state, an exciting theory suggests that sleep can solidify newly learned memories by rewiring the architecture of brain.

Emerging neuroscience evidence also indicates that sleep can intelligently associate and integrate new memories together, performing a kind of "sleep-dependent alchemy." This phenomenon may fuel creative human insights, often reflected in dream content.

In addition to memory benefits, recent findings also suggest that sleep can "refresh" emotional brain reactivity, smoothing away the rough edges from our prior waking concerns, thereby allowing rational next-day decisions.

Exploring the mind of a killer

Psychopathic killers are the basis for some must-watch TV, but what really makes them tick? Neuroscientist Jim Fallon talks about brain scans and genetic analysis that may uncover the rotten wiring in the nature (and nurture) of murderers. In a too-strange-for-fiction twist, he shares a fascinating family history that makes his work chillingly personal.

Getting by on six hours of sleep?

The Transcriptional Repressor DEC2 Regulates Sleep Length in Mammals
Ying He, Christopher R. Jones, Nobuhiro Fujiki, Ying Xu, Bin Guo, Jimmy L. Holder, Jr., Moritz J. Rossner, Seiji Nishino, Ying-Hui Fu
Science 14 August 2009:
Vol. 325. no. 5942, pp. 866 - 870

Sleep deprivation can impair human health and performance. Habitual total sleep time and homeostatic sleep response to sleep deprivation are quantitative traits in humans. Genetic loci for these traits have been identified in model organisms, but none of these potential animal models have a corresponding human genotype and phenotype. We have identified a mutation in a transcriptional repressor (hDEC2-P385R) that is associated with a human short sleep phenotype. Activity profiles and sleep recordings of transgenic mice carrying this mutation showed increased vigilance time and less sleep time than control mice in a zeitgeber time– and sleep deprivation–dependent manner. These mice represent a model of human sleep homeostasis that provides an opportunity to probe the effect of sleep on human physical and mental health.

Extreme Sleep Durations Lead to Poor Quality of Life

Sleep Duration and Health-Related Quality of Life among Older Adults: A Population-Based Cohort in Spain
Raquel Faubel, Esther Lopez-Garcia, Pilar Guallar-Castillón, Teresa Balboa-Castillo, Juan Luis Gutiérrez-Fisac, José R. Banegas, Fernando Rodríguez-Artalejo
Volume: 32
Issue : 08
Pages : 1059-1068

Study Objectives:The few studies that have addressed the association between sleep duration and health-related quality of life (HRQL) were cross-sectional and small-sized, targeted young and middle-aged persons, and did not adjust for the main confounders.This study sought to examine the cross-sectional and longitudinal relationship between habitual sleep duration and HRQL in older adults.

Design: Prospective study conducted from 2001 through 2003. Sleep duration was self-reported in 2001, and HRQL was measured using the SF-36 questionnaire in 2001 and 2003. Analyses were adjusted for the main confounders.

Setting: Community-based study.

Participants: A cohort of 3834 persons representative of the non-institutionalized Spanish population aged 60 years and over.

Intervention: None.

Measurement and Results: In comparison with women who slept 7 hours, those with extreme sleep durations (≤ 5 or ≥ 10 h) reported worse scores on the SF-36 physical and mental scales in 2001. Among men, sleeping ≤ 5 h was associated with a worse score in the role-physical scale in 2001. The magnitude of most of these associations was comparable with the reduction in HRQL associated with aging 10 years. Sleep duration in 2001 failed to predict changes in HRQL between 2001 and 2003.

Conclusion:Extreme sleep durations are a marker of worse HRQL in the elderly.

2-stage models of sleep and memory

Evidence for 2-stage models of sleep and memory: Learning-dependent changes in spindles and theta in rats
Stuart M. Fogel, Carlyle T. Smithb, Richard J. Beninger
Brain Research Bulletin 79 (2009) 445–451

What processes are involved in the formation of enduring memory traces? Sleep has been proposed to play a role in memory consolidation and the present study provides evidence to support 2-stage models of sleep and memory including both non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. Previous research has shown REM sleep increases following avoidance learning and memory is impaired if REM deprivation occurs during these post-training periods indicating that REM sleep may have a role in memory consolidation processes. These discrete post-training periods have been termed REM sleep windows (RSWs). It is not known whether the electroencephalogram has unique characteristics during the RSW. Further investigation of the RSW was one of the primary goals of this study. We investigated the epidural-recorded electrophysiological learning-related changes following avoidance training in rats. Theta power increased in the learning group during the RSW, suggesting that theta is involved in memory consolidation during this period. Sleep spindles subsequently increased in slow wave sleep (SWS). The results suggest that both NREM and REM sleep are involved in sleep-dependent memory consolidation, and provide support for existing 2-stage models. Perhaps first theta increases to organize and consolidate material via hippocampal–neocortical dialogue, followed by subsequent refinement in the cortex by spindles during SWS.