Thalamic Influence on Slow Wave Slope Renormalization During Sleep.

OBJECTIVE: Slow waves are thought to mediate an overall reduction in synaptic strength during sleep. The specific contribution of the thalamus to this so-called synaptic renormalization is unknown. Thalamic stroke is associated with daytime sleepiness, along with changes to sleep electroencephalography and cognition, making it a unique "experiment of nature" to assess the relationship between sleep rhythms, synaptic renormalization, and daytime functions. METHODS: Sleep was studied by polysomnography and high-density electroencephalography over 17 nights in patients with thalamic (n = 12) and 15 nights in patients with extrathalamic (n = 11) stroke. Sleep electroencephalographic overnight slow wave slope changes and their relationship with subjective daytime sleepiness, cognition, and other functional tests were assessed. RESULTS: Thalamic and extrathalamic patients did not differ in terms of age, sleep duration, or apnea-hypopnea index. Conversely, overnight slope changes were reduced in a large cluster of electrodes in thalamic compared to extrathalamic stroke patients. This reduction was related to increased daytime sleepiness. No significant differences were found in other functional tests between the 2 groups. INTERPRETATION: In patients with thalamic stroke, a reduction in overnight slow wave slope change and increased daytime sleepiness was found. Sleep- and wake-centered mechanisms for this relationship are discussed. Overall, this study suggests a central role of the thalamus in synaptic renormalization. ANN NEUROL 2021;90:821-833.

Author Correction: Deep sleep maintains learning efficiency of the human brain.

This corrects the article DOI: 10.1038/ncomms15405.

Deep sleep maintains learning efficiency of the human brain.

It is hypothesized that deep sleep is essential for restoring the brain's capacity to learn efficiently, especially in regions heavily activated during the day. However, causal evidence in humans has been lacking due to the inability to sleep deprive one target area while keeping the natural sleep pattern intact. Here we introduce a novel approach to focally perturb deep sleep in motor cortex, and investigate the consequences on behavioural and neurophysiological markers of neuroplasticity arising from dedicated motor practice. We show that the capacity to undergo neuroplastic changes is reduced by wakefulness but restored during unperturbed sleep. This restorative process is markedly attenuated when slow waves are selectively perturbed in motor cortex, demonstrating that deep sleep is a requirement for maintaining sustainable learning efficiency.

Exercise reward induces appetitive 50-kHz calls in rats.

Rats express affective states by visible behaviors (like approach or flight) and through different kinds of ultrasonic vocalizations (USV). 50-kHz calls are thought to reflect positive affective states since they occur during rewarding situations like social play or palatable food. However, the effects of voluntary exercise on USV have not been investigated yet, although such exercise can serve as reward. To this aim, we gave young adult rats restricted daily access to a runway maze, where they could interact with either a movable (experimental group) or locked wheel (sedentary group) for 14days and we tested USV in anticipation of and during subsequent running. We also studied inter-individual differences in running, and relationships with USV, and rat-typical trait measures. The results showed that the experimental rats had to be separated into "runners" and "pseudorunners" since only runners performed true running, whereas pseudorunners hardly entered the wheel and turned it only with their forelimbs. This outcome seems to be related to subject-dependent differences in responding to novelty and in reward sensitivity, as indicated by pertinent screening tests, which we had performed prior to the 14days of wheel access. In the runway, our experimental and control groups did not differ in visible anticipatory behavior, like approach. Yet, only runners and sedentary rats displayed an increasing but similar amount of anticipatory USV, which is suggestive of a state of incentive anticipation of the coming wheel access. During exercise, only runners increased USV, probably indicating a highly positive emotional state. To conclude, voluntary exercise provides a promising tool to induce 50-kHz USV during and in anticipation of exercise. When performing such studies, possible individual differences between subjects have to be taken into account, and the actual wheel performance should carefully be controlled.