Adaptive and pathological inhibition of neuroplasticity associated with circadian rhythms and sleep.

Abstract

The circadian system organizes sleep and wake through imposing a daily cycle of sleep propensity on the organism. Sleep has been shown to play an important role in learning and memory. Apart from the daily cycle of sleep propensity, however, direct effects of the circadian system on learning and memory also have been well documented. Many mechanistic components of the memory consolidation process ranging from the molecular to the systems level have been identified and studied. The question that remains is how do these various processes and components work together to produce cycles of increased and decreased learning abilities, and why should there be times of day when neural plasticity appears to be restricted? Insights into this complex problem can be gained through investigations of the learning disabilities caused by circadian disruption in Siberian hamsters and by aneuploidy in Down syndrome mice. A simple working hypothesis that has been explored in this work is that the observed learning disabilities are due to an altered excitation/inhibition balance in the CNS. Excessive inhibition is the suspected cause of deficits in memory consolidation. In this paper we present the evidence that excessive inhibition in these cases of learning disability involves GABAergic neurotransmission, that treatment with GABA receptor inhibitors can reverse the learning disability, and that the efficacy of the treatment is time sensitive coincident with the major daily sleep phase, and that it depends on sleep. The evidence we present leads us to hypothesize that a function of the circadian system is to reduce neuroplasticity during the daily sleep phase when processes of memory consolidation are taking place.

Sleep-Dependent Potentiation in the Visual System Is at Odds with the Synaptic Homeostasis Hypothesis

“…Third, a strict interpretation of SHY is that sleep promotes cognitive functions exclusively through synaptic weakening-which is not supported by data from several labs indicative of sleep-dependent synaptic strengthening. 3,[12][13][14][15][16][17][18] Nonetheless, if further evidence was needed that SHY is highly influential in the field, one might cite the fact that discussion of our data has been centered on how it relates to SHY. As Dr. Heller correctly stated in his commentary, 1 our previous findings do not disprove SHY.…”

“…Because SHY has been so influential, two questions neuroscientists must ask are: (1) whether synaptic potentiation associated with novel learning can occur during sleep and, (2) whether synaptic potentiation, downscaling, or both are present in the context of naturally occurring sleep-dependent plasticity. The answer to the first question is "yes" -our lab and others 3,[12][13][14][15][16][17] have already provided substantial evidence that synaptic potentiation can occur during sleep instead of wake. The second question can only be answered with data from the brain in the context of experience-dependent plasticity, not with rigid adherence to one hypothesis about the function of sleep.…”

Sex-specific sleep patterns among university students in Lebanon: impact on depression and academic performance

“…The fundamental role of good sleep quality and quantity in information processing, learning, and memory consolidation is well established in the literature. 8 – 11 The impact of sleep pattern changes on academic performance has been widely investigated in young adult groups, including university students. In one study, Singleton and Wolfson 12 showed the difference in bedtime habits between weekdays and weekends of college students to be directly correlated with their grade point average (GPA).…”

Sleep Disorders in Mentally Retarded Children

“…Известно, что к числу важнейших функций сна у здо-ровых людей относится формирование памяти и пла-стичности мозга (т. е. способность нейронов приобре-тать устойчивые структурные и/или функциональные изменения в ответ на различные стимулы, в частности, связанные с обучением) [2][3][4]. У большинства млекопи-тающих, в т. ч. и у человека, продолжительность сна мак-симальна в период новорожденности, когда происходят быстрый рост и созревание структур головного мозга и формирование пластичности синапсов за счет их ремоделирования [5].…”