Emotions, Sleep & Memory

The riddle of experience vs. memory

noreply@blogger.com (Ninad Gujar) — Thu, 24 Nov 2011 01:15:00 +0000

Nobel laureate and founder of behavioral economics Daniel Kahneman talks about happiness from a perspective of experience and remembering.

Sleep depotentiates prior emotional experiences/painful memories

noreply@blogger.com (Ninad Gujar) — Thu, 24 Nov 2011 01:03:00 +0000

REM Sleep Depotentiates Amygdala Activity to Previous Emotional Experiences
Current Biology, 23 November 2011 (Link)
Els van der Helm, Justin Yao, Shubir Dutt, Vikram Rao, Jared M. Saletin, Matthew P. Walker

Highlights

Sleep decreases amygdala activity to prior waking emotional experiences
The amygdala decrease is associated with reestablished prefrontal connectivity
These neural changes are accompanied by overnight reductions in subjective reactivity
Reductions in both brain and behavioral reactivity are associated with REM physiology

Summary Clinical evidence suggests a potentially causal interaction between sleep and affective brain function; nearly all mood disorders display co-occurring sleep abnormalities, commonly involving rapid-eye movement (REM) sleep. Building on this clinical evidence, recent neurobiological frameworks have hypothesized a benefit of REM sleep in palliatively decreasing next-day brain reactivity to recent waking emotional experiences. Specifically, the marked suppression of central adrenergic neurotransmitters during REM (commonly implicated in arousal and stress), coupled with activation in amygdala-hippocampal networks that encode salient events, is proposed to (re)process and depotentiate previous affective experiences, decreasing their emotional intensity. In contrast, the failure of such adrenergic reduction during REM sleep has been described in anxiety disorders, indexed by persistent high-frequency electroencephalographic (EEG) activity; a candidate factor contributing to hyperarousal and exaggerated amygdala reactivity. Despite these neurobiological frameworks, and their predictions, the proposed benefit of REM sleep physiology in depotentiating neural and behavioral responsivity to prior emotional events remains unknown. Here, we demonstrate that REM sleep physiology is associated with an overnight dissipation of amygdala activity in response to previous emotional experiences, altering functional connectivity and reducing next-day subjective emotionality.

Preferential benefits of sleep

noreply@blogger.com (Ninad Gujar) — Thu, 24 Nov 2011 00:53:00 +0000

Sleep-Dependent Facilitation of Episodic Memory Details
PLoS ONE 6(11): e27421. doi:10.1371/journal.pone.0027421 (Link)
Els van der Helm, Ninad Gujar, Masaki Nishida, Matthew P. Walker

While a role for sleep in declarative memory processing is established, the qualitative nature of this consolidation benefit, and the physiological mechanisms mediating it, remain debated. Here, we investigate the impact of sleep physiology on characteristics of episodic memory using an item- (memory elements) and context- (contextual details associated with those elements) learning paradigm; the latter being especially dependent on the hippocampus. Following back-to-back encoding of two word lists, each associated with a different context, participants were assigned to either a Nap-group, who obtained a 120-min nap, or a No Nap-group. Six hours post-encoding, participants performed a recognition test involving item-memory and context-memory judgments. In contrast to item-memory, which demonstrated no between-group differences, a significant benefit in context-memory developed in the Nap-group, the extent of which correlated both with the amount of stage-2 NREM sleep and frontal fast sleep-spindles. Furthermore, a difference was observed on the basis of word-list order, with the sleep benefit and associated physiological correlations being selective for the second word-list, learned last (most proximal to sleep). These findings suggest that sleep may preferentially benefit contextual (hippocampal-dependent) aspects of memory, supported by sleep-spindle oscillations, and that the temporal order of initial learning differentially determines subsequent offline consolidation.

How Best to Optimize Memory

noreply@blogger.com (Ninad Gujar) — Wed, 02 Nov 2011 16:09:00 +0000

To sleep, to strive, or both: how best to optimize memory
PLoS One. 2011;6(7):e21737. Epub 2011 Jul 20. (Link)
Matthew A. Tucker, Sunny X. Tang, Amaka Uzoh, Alexandra Morgan, Robert Stickgold

While numerous studies have shown that a night of sleep profits memory relative to wake, we still have little understanding about what factors mediate this effect of sleep. A clear understanding of the dynamics of this effect of sleep beyond the initial night of sleep is also lacking. Here, we examined the effect of extrinsic rewards on sleep-dependent declarative memory processing across 12 and 24 hr training-retest intervals. Subjects were either paid based on their performance at retest ($1 for each correct answer), or received a flat fee for participation. After a 12 hr interval we observed pronounced benefits of both sleep and reward on memory. Over an extended 24 hr interval we found 1) that an initial night of sleep partially protects memories from subsequent deterioration during wake, and 2) that sleep blocks further deterioration, and may even have a restorative effect on memory, when it follows a full day of wake. Interestingly, the benefit imparted to rewarded (relative to unrewarded) stimuli was equal for sleep and wake subjects, suggesting that the sleeping brain may not differentially process rewarded information, relative to wake. However, looking at the overall impact of sleep relative to reward in this protocol, it was apparent that sleep both imparted a stronger mnemonic boost than reward, and provided a benefit to memory regardless of whether it occurred in the first or the second 12 hrs following task training.

The memory function of sleep

noreply@blogger.com (Ninad Gujar) — Tue, 01 Nov 2011 02:00:00 +0000

Nature Reviews Neuroscience 11, 114-126 (February 2010)
Susanne Diekelmann & Jan Born

Sleep has been identified as a state that optimizes the consolidation of newly acquired information in memory, depending on the specific conditions of learning and the timing of sleep. Consolidation during sleep promotes both quantitative and qualitative changes of memory representations. Through specific patterns of neuromodulatory activity and electric field potential oscillations, slow-wave sleep (SWS) and rapid eye movement (REM) sleep support system consolidation and synaptic consolidation, respectively. During SWS, slow oscillations, spindles and ripples - at minimum cholinergic activity - coordinate the re-activation and redistribution of hippocampus-dependent memories to neocortical sites, whereas during REM sleep, local increases in plasticity-related immediate-early gene activity - at high cholinergic and theta activity - might favour the subsequent synaptic consolidation of memories in the cortex.

Sleep deprivation impairs the accurate recognition of human emotions

noreply@blogger.com (Ninad Gujar) — Fri, 06 Aug 2010 17:58:00 +0000

Sleep. 2010 Mar 1;33(3):335-42.
van der Helm E, Gujar N, Walker MP.
Sleep and Neuroimaging Laboratory, Department of Psychology, University of California, Berkeley, CA 94720-1650, USA.

STUDY OBJECTIVES: Investigate the impact of sleep deprivation on the ability to recognize the intensity of human facial emotions.

DESIGN: Randomized total sleep-deprivation or sleep-rested conditions, involving between-group and within-group repeated measures analysis. SETTING: Experimental laboratory study.

PARTICIPANTS: Thirty-seven healthy participants, (21 females) aged 18-25 y, were randomly assigned to the sleep control (SC: n = 17) or total sleep deprivation group (TSD: n = 20).

INTERVENTIONS: Participants performed an emotional face recognition task, in which they evaluated 3 different affective face categories: Sad, Happy, and Angry, each ranging in a gradient from neutral to increasingly emotional. In the TSD group, the task was performed once under conditions of sleep deprivation, and twice under sleep-rested conditions following different durations of sleep recovery. In the SC group, the task was performed twice under sleep-rested conditions, controlling for repeatability.

MEASUREMENTS AND RESULTS: In the TSD group, when sleep-deprived, there was a marked and significant blunting in the recognition of Angry and Happy affective expressions in the moderate (but not extreme) emotional intensity range; differences that were most reliable and significant in female participants. No change in the recognition of Sad expressions was observed. These recognition deficits were, however, ameliorated following one night of recovery sleep. No changes in task performance were observed in the SC group.

CONCLUSIONS: Sleep deprivation selectively impairs the accurate judgment of human facial emotions, especially threat relevant (Anger) and reward relevant (Happy) categories, an effect observed most significantly in females. Such findings suggest that sleep loss impairs discrete affective neural systems, disrupting the identification of salient affective social cues.

Impair human episodic memory

noreply@blogger.com (Ninad Gujar) — Fri, 23 Jul 2010 14:28:00 +0000

Single pulse electrical stimulation of the hippocampus is sufficient to impair human episodic memory.
Neuroscience. 2010 Jul 16
Lacruz ME, Valentín A, Seoane JJ, Morris RG, Selway RP, Alarcón G.

They used the single pulse electrical stimulation (SPES) technique to investigate whether more localized stimulation of the hippocampus can affect human episodic memory. A recognition memory test including words, object drawings, abstract drawings and unfamiliar faces was performed without stimulation (baseline) or synchronized with single 1 ms electrical pulses applied to the left, right or both hippocampi in 12 epileptic patients investigated with bilateral depth electrodes. No differences were found in memory performance between baseline and unilateral stimulation, either in the total score or in material-specific scores. In contrast, bilateral stimulation was associated with a pronounced decrease in the median of total memory scores (57%), and of material-specific sub-scores for words (38%), geometrical drawings (81%) and faces (100%). Additional study of stimulation at presentation of stimuli (encoding) versus the recognition memory (retrieval) test phase, showed only reduction in memory at encoding. The results provide causal evidence that the hippocampi are necessary for supporting episodic memory. The induction of memory deficits by bilateral stimulation with parameters that do not induce effects when applied unilaterally suggests that recognition memory can be processed independently by the hippocampus on either hemisphere

Science of motivation

noreply@blogger.com (Ninad Gujar) — Wed, 06 Jan 2010 23:37:00 +0000

Dan Pink examines the puzzle of motivation, starting with a fact that social scientists know but most managers don't: Traditional rewards aren't always as effective as we think. Listen for illuminating stories -- and maybe, a way forward.

The Episodic-inhibition hypothesis

noreply@blogger.com (Ninad Gujar) — Fri, 11 Dec 2009 15:20:00 +0000

Consolidation of Episodic Memories During Sleep: Long-Term Effects of Retrieval Practice
Psychological Science OnlineFirst, published on November 23, 2009 as doi:10.1177/0956797609354074
Mihály Racsmány, Martin A. Conway, and Gyula Demeter

Two experiments investigated the long-term effects of retrieval practice. In the retrieval-practice procedure, selected items from a previously studied list are repeatedly recalled. The typical retrieval-practice effects are considerably enhanced memory for practiced items accompanied by low levels of recall, relative to baseline, for previously studied items that are associated with the practiced items but were not themselves practiced. The two experiments demonstrated that the former effect persisted over 12 hr; the latter effect also persisted over 12 hr, but only if a period of nocturnal sleep occurred during the retention interval. We propose that consolidation processes occurring during sleep, and possibly featuring some form of offline rehearsal, mediate these long-term effects of retrieval practice.

More faithful memories for those experiences

noreply@blogger.com (Ninad Gujar) — Fri, 11 Dec 2009 15:20:00 +0000

Awake replay of remote experiences in the hippocampus
Nature Neuroscience Volume 12, Number 7, July 2009
Published online at http://www.nature.com/natureneuroscience
Mattias P Karlsson & Loren M Frank

Hippocampal replay is thought to be essential for the consolidation of event memories in hippocampal-neocortical networks. Replay is present during both sleep and waking behavior, but although sleep replay involves the reactivation of stored representations in the absence of specific sensory inputs, awake replay is thought to depend on sensory input from the current environment. Here, we show that stored representations are reactivated during both waking and sleep replay. We found frequent awake replay of sequences of rat hippocampal place cells from a previous experience. This spatially remote replay was as common as local replay of the current environment and was more robust when the rat had recently been in motion than during extended periods of quiescence. Our results indicate that the hippocampus consistently replays past experiences during brief pauses in waking behavior, suggesting a role for waking replay in memory consolidation and retrieval.

Growing Older Does Not Mean Sleeping Poorly

noreply@blogger.com (Ninad Gujar) — Fri, 11 Dec 2009 15:17:00 +0000

Recent Advances in Understanding Sleep and Sleep Disturbances in Older Adults
Growing Older Does Not Mean Sleeping Poorly
Association for Psychological Science Volume 18—Number 6
Michael V. Vitiello

Despite commonly held assumptions, growing older does not necessarily result in disturbed or unsatisfying sleep. There is no reason to assume, a priori, that the sleep of an older adult is necessarily problematic; in fact, many high-functioning older adults are satisfied with their sleep. When the various factors that can disrupt sleep— poor health, primary sleep disorders, poor sleep-hygiene practices (e.g., irregular sleep schedules and poor sleeping environments), and so on—are screened out, ‘‘optimally’’ or ‘‘successfully’’ aging older adults, assuming they remain healthy, can expect to experience little further change in their sleep and are not likely to experience excessive daytime sleepiness and the concomitant need to nap regularly during the day. Nevertheless, the majority of older adults, who are not optimally aging, suffer significant sleep disturbances from a variety of causes. Fortunately, our growing understanding of how sleep changes with aging and of the causes of these changes is informing ever-improving treatments for these disturbances, thereby helping to ensure that growing older does not mean sleeping poorly.

A theory of protoconsciousness

noreply@blogger.com (Ninad Gujar) — Tue, 27 Oct 2009 13:15:00 +0000

REM sleep and dreaming: towards a theory of protoconsciousness
Nature Reviews| Neuroscience volume 10 | November 2009 | 803
J. Allan Hobson

Dreaming has fascinated and mystified humankind for ages: the bizarre and evanescent qualities of dreams have invited boundless speculation about their origin, meaning and purpose. For most of the twentieth century, scientific dream theories were mainly psychological. Since the discovery of rapid eye movement (REM) sleep, the neural underpinnings of dreaming have become increasingly well understood, and it is now possible to complement the details of these brain mechanisms with a theory of consciousness that is derived from the study of dreaming. The theory advanced here emphasizes data that suggest that REM sleep may constitute a protoconscious state, providing a virtual reality model of the world that is of functional use to the development and maintenance of waking consciousness.

True or False?

noreply@blogger.com (Ninad Gujar) — Tue, 27 Oct 2009 13:13:00 +0000

How to Tell If a Particular Memory Is True or False
Daniel M. Bernstein and Elizabeth F. Loftus
Association for Psychological Science Volume 4—Number 4

How can you tell if a particular memory belonging to you or someone else is true or false? Cognitive scientists use a variety of techniques to measure groups of memories, whereas police, lawyers, and other researchers use procedures to determine whether an individual can be believed or not. We discuss evidence from behavioral and neuroimaging studies and research on lying that have attempted to distinguish true from false memories.

We remember events, people, and places all the time, but how accurate are those memories? More specifically, how can we identify true memories from false ones? A majority of studies trying to answer this question have tended to focus on one of several possible methods of analysis, concentrating on either groups of memories being reported (e.g., studying word lists and then remembering related words that were not included in the original lists) or the person who is reporting the memories (for example, using a battery of self-report questionnaires and behavioral assessments to predict who may be susceptible to forming false memories). In a new report, Daniel M. Bernstein and Elizabeth F. Loftus suggest that a combined approach — focusing on groups of memories, on the person who is remembering, and on the individual memory — along with taking advantage of a variety of research tools available (such as imaging devices, mathematical models, analysis techniques, and statistical methods) may be the best way to determine if a memory is truth or fiction.

Join the discussion here on APS.

Transform Your Mind, Change Your Brain

noreply@blogger.com (Ninad Gujar) — Fri, 02 Oct 2009 03:34:00 +0000

In this talk, Richard J. Davidson explores recent scientific research on the neuroscience of positive human qualities and how they can be cultivated through contemplative practice. Distinctions among different forms of contemplative practices are introduced and shown to have different neural and behavioral consequences, as well as important consequences for physical health in both long-term and novice practitioners. New research also shows that meditation-based interventions delivered online can produce behavioral and neural changes. Collectively, this body of research indicates that we can cultivate adaptive neural changes and strengthen positive human qualities through systematic mental practice.

The Role of Sleep in Emotional Brain Processing

noreply@blogger.com (Ninad Gujar) — Wed, 23 Sep 2009 22:52:00 +0000

Cognitive neuroscience continues to build meaningful connections between affective behavior and human brain function. Within the biological sciences, a similar renaissance has taken place, focusing on the role of sleep in various neurocognitive processes and, most recently, on the interaction between sleep and emotional regulation. This review surveys an array of diverse findings across basic and clinical research domains, resulting in a convergent view of sleep-dependent emotional brain processing. On the basis of the unique neurobiology of sleep, the authors outline a model describing the overnight modulation of affective neural systems and the (re)processing of recent emotional experiences, both of which appear to redress the appropriate next-day reactivity of limbic and associated autonomic networks. Furthermore, a rapid eye movement (REM) sleep hypothesis of emotional-memory processing is proposed, the implications of which may provide brain-based insights into the association between sleep abnormalities and the initiation and maintenance of mood disturbances.

How we read each other's minds?

noreply@blogger.com (Ninad Gujar) — Wed, 23 Sep 2009 22:47:00 +0000

Sensing the motives and feelings of others is a natural talent for humans. But how do we do it? Here, Rebecca Saxe shares fascinating lab work that uncovers how the brain thinks about other peoples' thoughts -- and judges their actions.

Consolidation of Associative Memory

noreply@blogger.com (Ninad Gujar) — Wed, 26 Aug 2009 14:47:00 +0000

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

noreply@blogger.com (Ninad Gujar) — Wed, 26 Aug 2009 04:50:00 +0000

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

noreply@blogger.com (Ninad Gujar) — Fri, 14 Aug 2009 08:34:00 +0000

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?

noreply@blogger.com (Ninad Gujar) — Fri, 14 Aug 2009 08:06:00 +0000

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

noreply@blogger.com (Ninad Gujar) — Tue, 04 Aug 2009 17:47:00 +0000

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
Sleep
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

noreply@blogger.com (Ninad Gujar) — Mon, 03 Aug 2009 23:36:00 +0000

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.

Functional Brain Networks Organization

noreply@blogger.com (Ninad Gujar) — Thu, 30 Jul 2009 18:40:00 +0000

Functional Brain Networks Develop from a "Local to Distributed" Organization
Damien A. Fair, Alexander L. Cohen, Jonathan D. Power, Nico U. F. Dosenbach, Jessica A. Church,Francis M. Miezin, Bradley L. Schlaggar, Steven E. Petersen
PLoS Computational Biology | 1 May 2009 | Volume 5 | Issue 5 | e1000381

The mature human brain is organized into a collection of specialized functional networks that flexibly interact to support various cognitive functions. Studies of development often attempt to identify the organizing principles that guide the maturation of these functional networks. In this report, we combine resting state functional connectivity MRI (rs-fcMRI), graph analysis, community detection, and spring-embedding visualization techniques to analyze four separate networks defined in earlier studies. As we have previously reported, we find, across development, a trend toward ‘segregation’ (a general decrease in correlation strength) between regions close in anatomical space and ‘integration’ (an increased correlation strength) between selected regions distant in space. The generalization of these earlier trends across multiple networks suggests that this is a general developmental principle for changes in functional connectivity that would extend to large-scale graph theoretic analyses of large-scale brain networks. Communities in children are predominantly arranged by anatomical proximity, while communities in adults predominantly reflect functional relationships, as defined from adult fMRI studies. In sum, over development, the organization of multiple functional networks shifts from a local anatomical emphasis in children to a more "distributed" architecture in young adults. We argue that this "local to distributed" developmental characterization has important implications for understanding the development of neural systems underlying cognition. Further, graph metrics (e.g., clustering coefficients and average path lengths) are similar in child and adult graphs, with both showing "small-world"-like properties, while community detection by modularity optimization reveals stable communities within the graphs that are clearly different between young children and young adults. These observations suggest that early school age children and adults both have relatively efficient systems that may solve similar information processing problems in divergent ways.

Whats and Whens of sleep-dependent memory consolidation

noreply@blogger.com (Ninad Gujar) — Thu, 30 Jul 2009 18:36:00 +0000

The whats and whens of sleep-dependent memory consolidation
Susanne Diekelmann, Ines Wilhelm, Jan Born
Sleep Medicine Reviews (2009), doi:10.1016

Sleep benefits memory consolidation. The reviewed studies indicate that this consolidating effect is not revealed under all circumstances but is linked to specific psychological conditions. Specifically, we discuss to what extent memory consolidation during sleep depends on the type of learning materials, type of learning and retrieval test, different features of sleep and the subject population. Post-learning sleep enhances consolidation of declarative, procedural and emotional memories. The enhancement is greater for weakly than strongly encoded associations and more consistent for explicitly than implicitly encoded memories. Memories associated with expected reward gain preferentially access to sleep-dependent consolidation. For declarative memories, sleep benefits are more consistently revealed with recall than recognition procedures at retrieval testing. Slow wave sleep (SWS) particularly enhances declarative memories whereas rapid eye movement (REM) sleep preferentially supports procedural and emotional memory aspects. Declarative memory profits already from rather short sleep periods (1–2 h). Procedural memory profits seem more dose-dependent on the amount of sleep following the day after learning. Children’s sleep with high amounts of SWS distinctly enhances declarative memories whereas elderly and psychiatric patients with disturbed sleep show impaired sleep-associated consolidation often of declarative memories. Based on the constellation of psychological conditions identified we hypothesize that access to sleep-dependent consolidation requires memories to be encoded under control of prefrontal-hippocampal circuitry, with the same circuitry controlling subsequent consolidation during sleep.

Genetic and molecular regulation of sleep

noreply@blogger.com (Ninad Gujar) — Mon, 20 Jul 2009 16:29:00 +0000

The genetic and molecular regulation of sleep: from fruit flies to humans
Nature Reviews | Neuroscience Volume 10 | August 2009 | 549
Chiara Cirelli

It has been known for a long time that genetic factors affect sleep quantity and quality. Genetic screens have identified several mutations that affect sleep across species, pointing to an evolutionary conserved regulation of sleep. Moreover, it has also been recognized that sleep affects gene expression. These findings have given valuable insights into the molecular underpinnings of sleep regulation and function that might lead the way to more efficient treatments for sleep disorders.