A single, severe traumatic head injury, or repeated multiple concussions that are typical of collision sports, can result in chronic sleep disturbances that can persist several years after the incident. Recent studies describe the mechanisms that link sleep disturbance and neurodegeneration.
Concussions cause mechanical injury to the brain that has functional consequences. The sudden acceleration, deceleration, and or rotation of the head may cause axonal shearing or avulsion. This type of injury alters the functions of neural circuits that underlie mood, learning and memory abilities, and sleep. A large majority of brain trauma victims report trouble initiating and or maintaining sleep or sleeping for excessive periods of time. These symptoms may persist for several years after the injury due to the neurochemical changes that are induced by the trauma.
Repeated concussions may lead to excess accumulation of amyloid-β and τ-proteins, which are implicated in neurodegenerative disorders, such as Alzheimer’s disease. Sleep disturbances, even minor ones such as a single night of sleep deprivation, can result in the accumulation of toxic amyloid-β and τ-protein. The accumulation of amyloid-β and τ-proteins alone are also sufficient to disrupt slow-wave sleep. Head trauma initiates a vicious cycle of sleep disturbance leading to the accumulation of these proteins, which then leads to more sleep disturbance. One important phase of sleep, slow-wave sleep, appears critical for the clearance of amyloid-β and τ-protein by the brain’s glymphatic system. Most head trauma victims probably do not get enough slow-wave sleep.
A recent study examined various sleep parameters, including, total sleep time, difficulty to fall asleep, restlessness, time to wake after sleep onset, sleep efficiency, and how much each stage of sleep contributed to the overall night of sleeping, after head trauma in 896 athletes.
Sleep disturbances were commonly reported within a week of head trauma. Such disturbances included poor sleep quality, excessive daytime sleepiness, and perceived changes in sleep duration, with both sleeping longer and sleeping less being reported. There was an apparent dose-response relationship between the number of head traumas experienced and the severity of sleep disturbance reported. Although most of the athletes in this analysis were males, the study noted that females are more likely to report poor sleep quality following head trauma.
These changes are unfortunate given that good quality sleep may reduce the histological changes. Sleep scientists speculate that the brains of those people who reported sleeping longer than usual after head trauma may be trying to increase the amount of slow-wave sleep to maximize the glymphatic drainage. Conversely, those who report sleeping less than usual after head trauma may be susceptible to the loss of slow-wave sleep, which may be contributing to cognitive decline in later life.
Studies of head trauma victims have led to a better understanding of the connection between sleep quality, the deposition of toxic proteins, and the increased vulnerability to the development of age-related neurodegenerative diseases. Unfortunately, no clinical studies have yet identified effective ways to improve sleep quality in these victims.