Sleep Changes Post-Concussion
Approximately 50% of individuals experience sleep disturbances post concussion (Ontario Neurotrauma Foundation, 2018). For many there is a slightly increased need for sleep immediately following the onset of a concussion. Typically this period is short in duration, although it is possible for hypersomnia (increased sleep duration or excessive daytime sleepiness) to persist. The most common sleep impairments after sustaining a concussion include insomnia, circadian rhythm sleep disorders, and changes to sleep architecture (Jaffee et al., 2015).
Insomnia: is the difficulty initiating or maintaining sleep, or sleep that is non restorative, which then impacts daily functioning (American Psychiatric Association, 2013).
Circadian rhythm disorders: are essentially the altered timing and rhythm of sleep, which may stem from a mismatch between the body’s internal clock and our external 24 hour clock. There may be a change in the timing of melatonin secretion (Shekleton et al., 2010). One of the more common circadian rhythm disorders post-concussion is a delayed sleep phase, where sleep onset does not occur until much later than it would have pre-injury.
Changes in sleep architecture: can include deviations from the typical ratios of the sleep stages within a sleep cycle e.g. more or less deep sleep.
Other sleep disturbances are also possible post-concussion, such as parasomnias (unusual behaviours during sleep or transition stages). The most commonly reported one is REM behaviour disorder in which patients lose the normal muscle paralysis during the REM phase and this allows them to act out their dreams (Jaffee et al., 2015). Other disturbances that can occur are restless leg syndrome and disordered breathing during sleep (e.g. sleep apnea), both of which may occur in higher percentages in individuals post-concussion than individuals in the general population.
To this date specific research on the neurophysiological effects on sleep are limited, although, it is likely that the cause for these sleep disturbances is multifaceted.
1. Firstly, a concussion results in a cascade of neurotransmitters and can have very diffuse effects across the brain. There is a possibility that this cascade disrupt the sleep circuits in the brain due to the release of neurotransmitters involved in sleep-wake circuits (Jaffee et al., 2015), or possibly due endocrine effects (Lucke-Wold et al., 2015).
2. Secondly, the injury itself, may result in structural damage, damage to the neurons or axons, which can also impact sleep if in a region involved in the sleep-wake circuits (Jaffee et al., 2015).
3. Third, often due to the symptom burden, an individuals lifestyle and metabolic demands change after the concussion. As an efficient and adaptable system, the requirements for certain stages of sleep may change, or the individual may require more or less sleep.
Risk Factors for Post-Concussive Sleep Disorders
There are specific groups of individuals who are more likely to be affected by circadian issues post-concussion. Circadian issues are more common in concussion patients who have visual consequences, this is due to circadian rhythms depending on the visual system. Daylight is an important factor in aligning our internal clocks to the external 24 hour one. If vision impairments are present, especially photophobia, individuals may avoid light, and as a consequence the eyes may lose the ability to use light to entrain the circadian rhythm.
Other groups are also more likely to experience sleep disorder post-concussion. Milder injuries, as defined by less reported symptoms and lower symptom severity, are more likely to result in sleep disturbance (Lucke-Wold et al., 2015). There also may be an effect of mental health on sleep, as sleep disturbances may be secondary to symptoms of the concussion. As concussion sometimes results in the development of depression or anxiety, these conditions may also increase the risk of developing sleep disorders post concussion (Jaffee et al., 2015).
Prior to a concussion risk of developing a sleep disorder is higher if one falls into the following groups: female, older adults, and also a personal or family history of insomnia or sleep disorder (Ouellet, Savard,& Morin, 2004). Additionally a risk factors for developing a sleep disorders after a concussion include the specific symptoms of headache and dizziness (Hou et al., 2013).
The Brain During Sleep
While we sometimes consider sleep inactivity, sleep is an active process facilitated by the brain. Ultimately many different neural circuits are involved, the process is quite complex. Sleep is not one singular uniform state, cycles and stages change what is going on in the brain during these times. Divisions of sleep can be categorized into four or five stages of sleep, as sometimes deep sleep (stages three and four below) is grouped together. Typically one begins with NREM 1 and progresses sequentially through the NREM stages, sometimes going back to NREM 2 briefly, then REM sleep occurs. Individuals continue to cycle through these stage throughout the night until the final waking in the morning.
During this stage of sleep the individual is just beginning to fall asleep. This is a very light sleep, a very short stage, usually only lasting a few minutes. Your threshold for arousal is still high, so waking from this stage is much easier than waking from deep sleep. Muscle activity also begins to slow down to prepare for sleep. If we were to look at brain activity, using electroencephalogram (EEG) data, we would see activity very similar activity to waking.
During this stage of sleep we begin to see more change on an EEG, this is the stage with sleep spindles, and then the waves slightly slow down. Body temperature begins to lower and the heart rate and respiration also slow.
This stage is the beginning of deep sleep. Your threshold for arousal increases, essentially it becomes more difficult to wake you up, and brain activity begins to become more synchronous. We begin to see more of the delta waves (lower frequency activity) among the higher frequency waves.
This is the stage where, if we were to look at an EEG recording, we would see the lowest level of activity in the brain. It is called slow wave sleep because there is a lot of synchronous activity, the neurons fire together, and thus we see almost exclusively smooth delta waves. This is the phase of sleep most responsible for restoration. We generally get more of this slow wave sleep in the beginning of the night, during those first few cycles, and then the length of the slow wave periods decrease throughout the night. There are increases in the amount of slow wave sleep with sleep deprivation, and decreases with naps, so it is correlated with the drive to sleep, or homeostatic pressure
This is the last stage of the sleep cycle, it is named for the phenomenon of the rapid eye movement (REM) that occurs during this stage. REM sleep is interesting because it is so very different from the other stages of sleep. During REM your brain is very active, the neurons fire asynchronously, as they do during waking hours. We see increased neural activity in the sensory and visual areas, and increased metabolism in the cortex. Additionally, in REM sleep, there is muscle atonia, very little muscle activity, as the motor system is suppressed. Typically, this the stage of sleep associated with dreaming, although dreaming is controlled by different brain mechanisms and dreams can also occur in other sleep stages. Theories regarding the purpose of REM sleep include the possibility that REM plays a role in memory consolidation, but at this point more research is needed to tell us whether this is the case.
Sleep and Recovery
Getting adequate sleep could contribute to recovering from a concussion in several ways. It seems common wisdom that sleep is restorative, and one of the most popular hypotheses for why we need to sleep, is that sleep plays an important restorative function. We also generally have lower metabolism in the brain during sleep as synaptic activity approaches baseline during sleep reducing the energy expenditure in the brain. This lesser activity in the brain is conserving energy, which can then be used to promote healing and perhaps adequate sleep does promote neurological recovery after a concussion (Jaffee et al., 2015). Finally, we do know that a lack of sleep can have harmful impacts on health and wellbeing, daily functioning, cognition, and mood (Ouellet et al., 2004). Therefore treating sleep disturbance can help reduce the additional negative effects on health and help promote rehabilitation.
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