Sleep Oscillations in Space

Since the early days of human spaceflight astronauts have reported and complained about sleep deficiency and fatigue during missions [1]. These sleep disturbances might be in part due to environmental factors such as noise, temperature and light intensity interfering with astronauts' sleep maintenance. It is well established that sleep loss is associated with poor health and performance decrements, both of which are crucial for space missions [2,3].

Polysomnographic data recorded from astronauts during spaceflight has only been analyzed with respect to gross changes in sleep architecture [4,5,6]. However, neural oscillations during sleep have been associated with various detrimental effects in ground based studies that also occur during human spaceflight. For this reason we are re-analyzing the STS-90 and STS-95 data that was acquired by Dijk et al. (2001) with a special focus on investigating the characteristics of slow waves and sleep spindles.

Slow waves are hallmark neural oscillations predominantly occurring during N3, residing in a frequency range of 0.75 to 4 Hz. Slow waves are characterized by highly synchronized down-states and up-states corresponding to widespread, long-lasting hyperpolarization or depolarization of the slow oscillation generating neocortical neural populations. They have been related to memory consolidation, sleep-wake homeostasis and define the most stable sleep stage as assessed by arousal probability [7,8,9].

Sleep spindles are well studied 11 to 15 Hz neural oscillations defining stage two non-rapid eye movement (NREM) sleep [10,11]. Nested in slow waves' up-phases they also occur in NREM stage 3. Sleep spindles originate from the interplay of thalamic reticular nuclei neurons and thalamocortical neurons. Corticothalamic feedback loops synchronize these oscillations and make their waxing and waning amplitude of about 0.5 to 3 s duration detectable in the human electroencephalogram (EEG). Studies have verified the role of sleep spindles in memory consolidation, the process of transferring and integrating labile memories into a stable system of long-term memories [12,13]. Moreover, several investigations have implicated a sleep-protective function of sleep spindles [14,15,16].

Investigating these oscillations in collaboration with Dr. Laura Barger from the Brigham and Women's Hospital as well as Dr. Erin Flynn-Evans from NASA's Fatigue Countermeasure Laboratoy will hopefully yield new insights on sleep disturbances and sleep-related cognitive decrements during spaceflight, eventually enabling the development of novel countermeasures against observed sleep deficiencies.

References

1. Barger, L. K., Flynn-Evans, E. E., & Czeisler, C. A. (2014). Prevalence of Sleep Deficiency and Hypnotic Use Among Astronauts Before, During and After Spaceflight: An Observational Study. Lancet Neurol., 102(9), 1207–1211. https://doi.org/10.1016/S1474-4422(14)70122-X
2. Flynn-Evans, E., Gregory, K., Arsintescu, L., Whitmire, A., & Leveton, L. B. (2015). Evidence report: Risk of performance decrements and adverse health outcomes resulting from sleep loss, circadian desynchronization, and work overload in human health and performance risks of space exploration missions NASA human research roadmap. Retrieved from https://humanresearchroadmap.nasa.gov/evidence/reports/sleep.pdf
3. Van Dongen, H. P. A., Maislin, G., Mullington, J. M., & Dinges, D. F. (2003). The cumulative cost of additional wakefulness: dose-response effects on neurobehavioral functions and sleep physiology from chronic sleep restriction and total sleep deprivation. Sleep, 26(2), 117–26. https://academic.oup.com/sleep/article/26/2/117/2709164
4. Dijk, D. J., Neri, D. F., Wyatt, J. K., Ronda, J. M., Riel, E., Ritz-De Cecco, A., Hughes, R. J., Elliott, A. R., Prisk, G. K., West, J. B., & Czeisler, C. A. (2001). Sleep, performance, circadian rhythms, and light-dark cycles during two space shuttle flights. American Journal of Physiology - Regulatory, Integrative and Comparative Physiology, 281(5), R1647-R1664. https://doi.org/10.1152/ajpregu.2001.281.5.R1647
5. Gundel, A., Polyakov, V. V., & Zulley, J. (1997). The alteration of human sleep and circadian rhythms during spaceflight. Journal of sleep research, 6(1), 1-8. https://doi.org/10.1046/j.1365-2869.1997.00028.x
6. Monk, T. H., Buysse, D. J., Billy, B. D., Kennedy, K. S., & Willrich, L. M. (1998). Sleep and circadian rhythms in four orbiting astronauts. Journal of biological rhythms, 13(3), 188-201. https://doi.org/10.1177/074873098129000039
7. Steriade, M. (2006). Grouping of brain rhythms in corticothalamic systems. Neuroscience, 137(4), 1087-1106. https://doi.org/10.1016/j.neuroscience.2005.10.029
8. Tononi, G., & Cirelli, C. (2014). Sleep and the price of plasticity: from synaptic and cellular homeostasis to memory consolidation and integration. Neuron, 81(1), 12-34. https://doi.org/10.1016/j.neuron.2013.12.025
9. Buxton, O. M., Ellenbogen, J. M., Wang, W., Carballeira, A., O'Connor, S., Cooper, D., ... & Solet, J. M. (2012). Sleep disruption due to hospital noises: a prospective evaluation. Annals of internal medicine, 157(3), 170-179. doi: 10.7326/0003-4819-156-12-201208070-00472
10. De Gennaro, L., & Ferrara, M. (2003). Sleep spindles: an overview. Sleep medicine reviews, 7(5), 423-440. https://doi.org/10.1053/smrv.2002.0252
11. Purcell, S. M., Manoach, D. S., Demanuele, C., Cade, B. E., Mariani, S., Cox, R., Panagiotaropoulou, G., Saxena, R., Pan, J. Q., Smoller, J. W., Redline, S. & Stickgold, R. (2017). Characterizing sleep spindles in 11,630 individuals from the National Sleep Research Resource. Nature communications, 8, 15930. doi: 10.1038/ncomms15930
12. Mednick, S. C., McDevitt, E. A., Walsh, J. K., Wamsley, E., Paulus, M., Kanady, J. C., & Drummond, S. P. (2013). The critical role of sleep spindles in hippocampal-dependent memory: a pharmacology study. Journal of Neuroscience, 33(10), 4494-4504. doi: https://doi.org/10.1523/JNEUROSCI.3127-12.2013
13. Schabus, M., Gruber, G., Parapatics, S., Sauter, C., Klösch, G., Anderer, P., Klimesch, W., Saletu, B. & Zeitlhofer, J. (2004). Sleep spindles and their significance for declarative memory consolidation. Sleep, 27(8), 1479-1485. https://doi.org/10.1093/sleep/27.7.1479
14. Dang-Vu, T. T., McKinney, S. M., Buxton, O. M., Solet, J. M., & Ellenbogen, J. M. (2010). Spontaneous brain rhythms predict sleep stability in the face of noise. Current Biology, 20(15). https://doi.org/10.1016/j.cub.2010.06.032
15. Kim, A., Latchoumane, C., Lee, S., Kim, G. B., Cheong, E., Augustine, G. J., & Shin, H.-S. (2012). Optogenetically induced sleep spindle rhythms alter sleep architectures in mice. Proceedings of the National Academy of Sciences, 109(50), 20673–20678. https://doi.org/10.1073/pnas.1217897109
16. Wimmer, R. D., Astori, S., Bond, C., Rovo, Z., Chatton, J.-Y., Adelman, J. P., Franken, P., Luthi, A. (2012). Sustaining sleep spindles through enhanced SK2 channel activity consolidates sleep and elevates arousal threshold. https://doi.org/10.1523/JNEUROSCI.2313-12.2012