Human brain patterns underlying vigilant attention: impact of sleep debt, circadian phase and attentional engagement

Abstract Sleepiness and cognitive function vary over the 24-h day due to circadian and sleep-wake-dependent mechanisms. However, the underlying cerebral hallmarks associated with these variations remain to be fully established. Using functional magnetic resonance imaging (fMRI), we investigated brain responses associated with circadian and homeostatic sleep-wake-driven dynamics of subjective sleepiness throughout day and night. Healthy volunteers regularly performed a psychomotor vigilance task (PVT) in the MR-scanner during a 40-h sleep deprivation (high sleep pressure) and a 40-h multiple nap protocol (low sleep pressure). When sleep deprived, arousal-promoting thalamic activation during optimal PVT performance paralleled the time course of subjective sleepiness with peaks at night and troughs on the subsequent day. Conversely, task-related cortical activation decreased when sleepiness increased as a consequence of higher sleep debt. Under low sleep pressure, we did not observe any significant temporal association between PVT-related brain activation and subjective sleepiness. Thus, a circadian modulation in brain correlates of vigilant attention was only detectable under high sleep pressure conditions. Our data indicate that circadian and sleep homeostatic processes impact on vigilant attention via specific mechanisms; mirrored in a decline of cortical resources under high sleep pressure, opposed by a subcortical “rescuing” at adverse circadian times

Sleep After Traumatic Brain Injury

Traumatic brain injury (TBI) is an important cause of death and disability at all ages in the world. Complete functional recovery is not always complete, and, often, persistent symptoms may last for a long time. Sleep disorders and sleep-wake alterations are among the most common complications both in the acute and chronic phases after the trauma, and they may have a negative impact on daily activities and on quality of life of these patients. Sleep and sleep-wake cycle are not always carefully assessed in patients after TBI, they are overlooked, and often patients have a persistent excessive daytime sleepiness, even for years after the TBI, without receiving a proper diagnosis and treatment. Moreover, scientific evidence has been provided for the role of sleep in neuroprotection and recovery after brain injury; hence, promoting an optimal sleep function and early diagnosing and treating sleep disorders may be helpful for rehabilitation and functional recovery of patients after TBI