THE RECOVERY OF SLEEP OSCILLATIONS IN ACUTE TO CHRONIC TRAUMATIC BRAIN INJURY

Abstract Introduction Slow waves and spindles are essential oscillations occurring during NREM sleep that may be disrupted by moderate to severe traumatic brain injury (TBI). We investigated these oscillations in the acute and chronic trauma stage. Methods Four groups were tested with whole-night polysomnography: hospitalized patients with acute TBI (n=10, 29.7±13.8y) or severe orthopedic injuries (n=15, 39.9±17.1y), chronic TBI including 9 returning from the acute TBI group (n=43, 31.9±13.5y), and healthy controls (n=36, 30.5±12.7y). Characteristics for slow waves (density, amplitude, slope, frequency, duration) and spindles (density, amplitude, frequency, duration) were quantified over N2 and N3 sleep for the first three sleep cycles, and groups were compared using one-way ANOVAs. Results One-way ANOVAs showed group effects only for slow wave density (F=4.11 to 6.04, p=0.009 to 0.0008)) and spindle density (F=3.3 to 8.8, p=0.02 to 0.00003). These effects were present for the 2nd and 3rd sleep cycles, but not the 1st. More specifically, slow wave density in acute TBI was higher than in controls, and returned to normal levels in the chronic stage. Conversely, spindle density in acute TBI was lower than in controls and returned to normal levels in the chronic stage. No group difference was observed for the orthopedic group. Conclusion Our results suggest that immediately after a severely disruptive event such as a TBI, the brain needs additional deeper sleep to recover, resulting in more slow waves but also in less spindles. These changes are only present in the 2nd and 3rd sleep cycles, reflecting an absence of the expected dissipation of slow waves, which may suggest increased homeostatic sleep pressure due to the brain injury. Limits to interpretation include the hospital environment and medication, but the absence of changes in the orthopedic group under similar conditions emphasizes the effect of the brain injury itself. Support Canadian Institutes of Health Research (CIHR) and Fonds de Recherche Québec-Santé (FRQS)