Free recall of word lists under total sleep deprivation and after recovery sleep

Memory impairments observed after a half night sleep restriction are not mediated by working memory, attention, or inhibitory control mechanisms

Sleep restriction is a growing issue in our modern society and thus it is crucial to uncover its neurocognitive consequences. Especially declarative memory is negatively affected by sleep loss due to its critical dependence on the hippocampus, a brain area known to be susceptible to sleep loss. Studies have shown that even a half night sleep restriction is sufficient to induce impairments in a range of hippocampus-dependent forms of memory. Nevertheless, memory performance is, at least to some extent, dependent on other cognitive functions. The aim of the current study was to reveal whether memory deficits observed after one night sleep deprivation, as observed in animal studies, translate to man, and whether these effects are mediated by impairments in other cognitive domains. We hypothesized that the memory paradigms would be affected but that, due to the short nature of the sleep restriction, this effect would not be mediated by other cognitive functions. To this end, fifty-five healthy participants conducted a test battery containing paradigms measuring verbal learning, spatial memory, attention, working memory, and response inhibition after a night of regular sleep or acute partial sleep restriction. The results of the study showed an impairment in both hippocampus-dependent memory tests, while no negative consequences of sleep deprivation were revealed on the other cognitive domains. In conclusion, our data indicate that the observed deficit in memory performance after a half night sleep deprivation is not mediated by impairments in attention (alerting, orienting, and executive control), working memory, or motor inhibitory control mechanisms.

Investigation of the structural changes in the hippocampus and prefrontal cortex using FTIR spectroscopy in sleep deprived mice

Sleep is a basic, physiological requirement for living things to survive and is a process that covers one third of our lives. Melatonin is a hormone that plays an important role in the regulation of sleep. Sleep deprivation affect brain structures and functions. Sleep deprivation causes a decrease in brain activity, with particularly negative effects on the hippocampus and prefrontal cortex. Despite the essential role of protein and lipids vibrations, polysaccharides, fatty acid side chains functional groups, and ratios between amides in brain structures and functions, the brain chemical profile exposed to gentle handling sleep deprivation model versus Melatonin exposure remains unexplored. Therefore, the present study, aims to investigate a molecular profile of these regions using FTIR spectroscopy measurement's analysis based on lipidomic approach with chemometrics and multivariate analysis to evaluate changes in lipid composition in the hippocampus, prefrontal regions of the brain. In this study, C57BL/6J mice were randomly assigned to either the control or sleep deprivation group, resulting in four experimental groups: Control (C) (n = 6), Control + Melatonin (C + M) (n = 6), Sleep Deprivation (S) (n = 6), and Sleep Deprivation + Melatonin (S + M) (n = 6). Interventions were administered each morning via intraperitoneal injections of melatonin (10 mg/kg) or vehicle solution (%1 ethanol + saline), while the S and S + M groups underwent 6 h of daily sleep deprivation from using the Gentle Handling method. All mice were individually housed in cages with ad libitum access to food and water within a 12-hour light-dark cycle. Results presented that the brain regions affected by insomnia. The structure of phospholipids, changed. Yet, not only changes in lipids but also in amides were noticed in hippocampus and prefrontal cortex tissues. Additionally, FTIR results showed that melatonin affected the lipids as well as the amides fraction in cortex and hippocampus collected from both control and sleep deprivation groups.

Organization and Priming of Long-term Memory Representations with Two-phase Plasticity

Background / Introduction

In recurrent neural networks in the brain, memories are represented by so-called Hebbian cell assemblies. Such assemblies are groups of neurons with particularly strong synaptic connections formed by synaptic plasticity and consolidated by synaptic tagging and capture (STC). To link these synaptic mechanisms to long-term memory on the level of cognition and behavior, their functional implications on the level of neural networks have to be understood.

Methods

We employ a biologically detailed recurrent network of spiking neurons featuring synaptic plasticity and STC to model the learning and consolidation of long-term memory representations. Using this, we investigate the effects of different organizational paradigms, and of priming stimulation, on the functionality of multiple memory representations. We quantify these effects by the spontaneous activation of memory representations driven by background noise.

Results

We find that the learning order of the memory representations significantly biases the likelihood of activation towards more recently learned representations, and that hub-like overlap structure counters this effect. We identify long-term depression as the mechanism underlying these findings. Finally, we demonstrate that STC has functional consequences for the interaction of long-term memory representations: 1. intermediate consolidation in between learning the individual representations strongly alters the previously described effects, and 2. STC enables the priming of a long-term memory representation on a timescale of minutes to hours.

Conclusion

Our findings show how synaptic and neuronal mechanisms can provide an explanatory basis for known cognitive effects.

Quantifying Cognitive Impairment After Sleep Deprivation at Different Times of Day: A Proof of Concept Using Ultra-Short Smartphone-Based Tests

Cognitive functioning is known to be impaired following sleep deprivation and to fluctuate depending on the time of day. However, most methods of assessing cognitive performance remain impractical for environments outside of the lab. This study investigated whether 2-min smartphone-based versions of commonly used cognitive tests could be used to assess the effects of sleep deprivation and time of day on diverse cognitive functions. After three nights of normal sleep, participants (N = 182) were randomised to either one night of sleep deprivation or a fourth night of normal sleep. Using the Karolinska WakeApp (KWA), participants completed a battery of 2-min cognitive tests, including measures of attention, arithmetic ability, episodic memory, working memory, and a Stroop test for cognitive conflict and behavioural adjustment. A baseline measurement was completed at 22:30 h, followed by three measurements the following day at approximately 08:00 h, 12:30 h, and 16:30 h. Sleep deprivation led to performance impairments in attention, arithmetic ability, episodic memory, and working memory. No effect of sleep deprivation was observed in the Stroop test. There were variations in attention and arithmetic test performance across different times of day. The effect of sleep deprivation on all cognitive tests was also found to vary at different times of day. In conclusion, this study shows that the KWA's 2-min cognitive tests can be used to detect cognitive impairments following sleep deprivation, and fluctuations in cognitive performance relating to time of day. The results demonstrate the potential of using brief smartphone-based tasks to measure a variety of cognitive abilities within sleep and fatigue research.

Two nights of recovery sleep restores hippocampal connectivity but not episodic memory after total sleep deprivation

Sleep deprivation significantly impairs a range of cognitive and brain function, particularly episodic memory and the underlying hippocampal function. However, it remains controversial whether one or two nights of recovery sleep following sleep deprivation fully restores brain and cognitive function. In this study, we used functional magnetic resonance imaging (fMRI) and examined the effects of two consecutive nights (20-hour time-in-bed) of recovery sleep on resting-state hippocampal connectivity and episodic memory deficits following one night of total sleep deprivation (TSD) in 39 healthy adults in a controlled in-laboratory protocol. TSD significantly reduced memory performance in a scene recognition task, impaired hippocampal connectivity to multiple prefrontal and default mode network regions, and disrupted the relationships between memory performance and hippocampal connectivity. Following TSD, two nights of recovery sleep restored hippocampal connectivity to baseline levels, but did not fully restore memory performance nor its associations with hippocampal connectivity. These findings suggest that more than two nights of recovery sleep are needed to fully restore memory function and hippocampal-memory associations after one night of total sleep loss.

Construção e Avaliação para 15 Listas de Palavras Baseadas no Paradigma Deese-Roediger-McDermott

Resumo Com base nos estudos conduzidos de acordo com o paradigma Deese-Roediger-McDermott (DRM), em quais palavras de uma lista tendem a evocar outros itens relacionados, utilizado em pesquisas de falsas memórias, neste estudo elaborou-se 15 listas de palavras semanticamente relacionadas para o português. Para a elaboração das listas, foram considerados critérios como frequência de palavras no corpus de português brasileiro e extensão de palavras. A pré-seleção guiada por características linguísticas visava controlar possíveis vieses por parte dos voluntários. Testes de associação semântica e concretude de palavras foram realizados para apurar a conveniência dos itens selecionados, e um teste de recordação livre foi conduzido para avaliar características de evocação. Sugerimos a utilização das listas de palavras em pesquisas que avaliem falsas memórias.

Effects of methamphetamine self-administration on actigraphy-based sleep parameters in rhesus monkeys

RATIONALE

Sleep disorders and substance abuse are highly comorbid. Although methamphetamine is a very commonly abused drug, to the best of our knowledge, no study has evaluated its effects on sleep during drug use and abstinence under well-controlled conditions in laboratory animals.

OBJECTIVES

The objective of this study was to examine the effects of methamphetamine self-administration on sleep-like measures in nonhuman primates.

METHODS

Adult male rhesus monkeys (Macaca mulatta; n = 4) self-administered methamphetamine (0.01 and 0.03 mg/kg/injection, i.v.) under a fixed-ratio 20 schedule of reinforcement (60-min sessions once a day, 5 days per week) for 5 weeks. Sleep-like measures were evaluated with Actiwatch monitors before, during, and after each period of drug self-administration.

RESULTS

Both doses of methamphetamine reliably maintained self-administration. Methamphetamine (0.03 mg/kg) increased derived measures of latency to sleep onset and sleep fragmentation, and decreased sleep efficiency compared to abstinence, and higher methamphetamine intake predicted worse sleep quality. However, sleep normalized immediately after the discontinuation of methamphetamine self-administration.

CONCLUSIONS

Methamphetamine markedly disrupted sleep-like measures; however, methamphetamine self-administration did not disrupt sleep quality during subsequent periods of drug abstinence.