Sleep Difficulties in Swiss Elite Athletes.

For athletes, sleep is essential for recovery and performance. Yet, up to two-thirds of athletes report poor sleep quality. Comprehensive data across all sports disciplines on the underlying causes of sleep problems are missing. We reanalyzed a data set of N = 1004 Swiss top athletes across an extensive array of 88 sports to gain knowledge on the specific deficits in sleep health with respect to gender, sport classes, sport-related factors, and well-being. We found that 18% of athletes were affected by at least two out of five high-risk sleep factors: 9% of athletes slept less than 6 h per day, 30% were dissatisfied with their sleep, 17% showed problems falling asleep within 30 min, 18% of athletes reported difficulty maintaining sleep more than three times a week, and 6% of athletes used sleeping pills more than once a week. We found sleep health strongly linked to overall well-being and mental health (22% showed at least moderate symptoms of either depression or anxiety). Therefore, screening and treating sleep disorders might effectively improve mental health and general well-being as well as performance among athletes around the globe.

Sleep and conditioning of the siphon withdrawal reflex in Aplysia.

Sleep is essential for memory consolidation after learning as shown in mammals and invertebrates such as bees and flies. Aplysia californica displays sleep, and sleep in this mollusk was also found to support memory for an operant conditioning task. Here, we investigated whether sleep in Aplysia is also required for memory consolidation in a simpler type of learning, i.e. the conditioning of the siphon withdrawal reflex. Two groups of animals (Wake, Sleep, each n=11) were conditioned on the siphon withdrawal reflex, with the training following a classical conditioning procedure where an electrical tail shock served as the unconditioned stimulus (US) and a tactile stimulus to the siphon as the conditioned stimulus (CS). Responses to the CS were tested before (pre-test), and 24 and 48 h after training. While Wake animals remained awake for 6 h after training, Sleep animals had undisturbed sleep. The 24 h test in both groups was combined with extinction training, i.e. the extended presentation of the CS alone over two blocks. At the 24 h test, siphon withdrawal duration in response to the CS was distinctly enhanced in both Sleep and Wake groups with no significant difference between groups, consistent with the view that consolidation of a simple conditioned reflex response does not require post-training sleep. Surprisingly, extinction training did not reverse the enhancement of responses to the CS. On the contrary, at the 48 h test, withdrawal duration in response to the CS was even further enhanced across both groups. This suggests that processes of sensitization, an even simpler non-associative type of learning, contributed to the withdrawal responses. Our study provides evidence for the hypothesis that sleep preferentially benefits consolidation of more complex learning paradigms than conditioning of simple reflexes.

Wakefulness rather than sleep benefits extinction of an inhibitory operant conditioning memory in Aplysia.

Sleep enhances memory consolidation which has been shown in mammals as well as in invertebrates, like bees and Drosophila. The current study is part of a series of experiments examining whether this memory function of sleep is preserved in Aplysia with an even simpler nervous system. Previous work showed that Aplysia sleep and that sleep after training supports memory on an inhibitory conditioning task ('learning that food is inedible', LFI). Here, we tested whether sleep in Aplysia would also support memory for an extinction learning on the LFI task. Following Acquisition in which animals learned that netted food is inedible, two groups of animals, a Sleep group (n = 15) and a Wake group (n = 16) underwent extinction training. After a 17-hour Retention interval which contained either regular nocturnal sleep or daytime wakefulness (supported by sleep deprivation) animals were retested on the LFI task. Contrary to our hypothesis, the Wake animals showed significantly prolonged food intake behavior on the LFI, indicating that extinction memory in these animals was better than in the Sleep animals. Performance of a control group not subjected to extinction training, ruled out that the superior extinction performance of Wake animals merely reflected forgetting over time of the LFI memory, and also excluding a possible circadian confound. We speculate that wakefulness mainly acts by accelerating active forgetting of the LFI memory after it was labialized through extinction training, thereby facilitating the re-emergence of the original innate behavior of food intake.

Sleep supports inhibitory operant conditioning memory in Aplysia.

Sleep supports memory consolidation as shown in mammals and invertebrates such as bees and Drosophila. Here, we show that sleep's memory function is preserved in Aplysia californica with an even simpler nervous system. Animals performed on an inhibitory conditioning task ("learning that a food is inedible") three times, at Training, Retrieval 1, and Retrieval 2, with 17-h intervals between tests. Compared with Wake animals, remaining awake between Training and Retrieval 1, Sleep animals with undisturbed post-training sleep, performed significantly better at Retrieval 1 and 2. Control experiments testing retrieval only after ∼34 h, confirmed the consolidating effect of sleep occurring within 17 h after training.

Sleep and memory in mammals, birds and invertebrates.

Sleep supports memory consolidation. Based on studies in mammals, sleep-dependent consolidation has been conceptualized as 'active system consolidation'. During waking, information is encoded into an initial store (hippocampus). During subsequent sleep, some of the newly encoded memories are selected to be reactivated and redistributed toward networks serving as long-term store (e.g., neocortex), whereby memories become transformed into more general, schema-like representations. Here we asked whether sleep in non-mammalian species might play a comparable role for memory. The literature review revealed that sleep produces enhancing effects on memory in all non-mammalian species studied. Furthermore, across species some of the hallmarking features of active system consolidation were identified: Studies of filial imprinting in chicks suggest that a redistribution of imprinting memory toward long-term storage sites occurs during sleep; song learning in birds appears to be driven by reactivations of song representations during sleep; studies of bees demonstrated the selectivity of sleep-dependent consolidation, benefiting extinction but not original classical conditioning. Although overall fragmentary, first evidence in non-mammalian species suggests active system consolidation might be an evolutionary conserved function of sleep.

Characterization of sleep in Aplysia californica.

STUDY OBJECTIVE: To characterize sleep in the marine mollusk, Aplysia californica. DESIGN: Animal behavior and activity were assessed using video recordings to measure activity, resting posture, resting place preference, and behavior after rest deprivation. Latencies for behavioral responses were measured for appetitive and aversive stimuli for animals in the wake and rest states. SETTING: Circadian research laboratory for Aplysia. PATIENTS OR PARTICIPANTS: A. californica from the Pacific Ocean. INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: Aplysia rest almost exclusively during the night in a semi-contracted body position with preferential resting locations in the upper corners of their tank. Resting animals demonstrate longer latencies in head orientation and biting in response to a seaweed stimulus and less frequent escape response steps following an aversive salt stimulus applied to the tail compared to awake animals at the same time point. Aplysia exhibit rebound rest the day following rest deprivation during the night, but not after similar handling stimulation during the day. CONCLUSIONS: Resting behavior in Aplysia fulfills all invertebrate characteristics of sleep including: (1) a specific sleep body posture, (2) preferred resting location, (3) reversible behavioral quiescence, (4) elevated arousal thresholds for sensory stimuli during sleep, and (5) compensatory sleep rebound after sleep deprivation.