Concussions Can Impair Emotional Processing During Sleep Contributing to Chronic Mood Disturbance
As discussed in prior posts on this blog, sleep alterations are commonly found after a concussion or other traumatic brain injury, both short term and in some cases long term. One of the most well documented impacts of concussion, also discussed in prior posts, is an increased risk of mood disturbances, including depression, increased anxiety and increased risk of suicide. In recent years researchers have turned to sleep studies to explore the connection between these symptoms.
There is substantial evidence in the literature of the role healthy sleep plays in the “consolidation” of emotional memories. At first blush, this research is counter-intuitive. If sleep “consolidates” emotional memories, doesn’t this have the potential to increase rather than decrease mood disturbance? The answer appears to be that, although sleep preserves memory of events associated with emotional experience, at the same time it weakens the emotional “charge” coating the experience (referred to in the literature as “valence”) in a process called “habituation.” As one researcher hypothesized, “we sleep to forget the emotional tone, yet sleep to remember the tagged information.”
It is increasingly understood that sleep both integrates the emotional memory and simultaneously inhibits involuntary retrieval of negative memories. Every major psychiatric disorder is associated with a high prevalence of sleep disturbance. The evidence indicates that sleep alterations are not just a side effect of psychopathology, they actively contribute to and maintain dysfunction.
Against this backdrop, researchers at the University of Massachusetts, in a study recently published in SLEEP, examined whether students with a history of concussion at least a year earlier demonstrated a reduction in sleep dependent emotional memory consolidation and whether the students with a history of concussion showed less “habituation” to negative images. They also compared the quality of sleep between the two groups. Mantua, et. al. “Mild Traumatic Brain Injury Chronically Impairs Sleep and Wake-Dependent Emotional Processing” SLEEP, Vol.40, No.6, 2017.
Even though it had been at least a year since concussion, the concussion group showed less rapid eye movements, longer REM latency (the length of time before REM sleep), and more sleep complaints. These findings suggest that sleep disruption can be long term, even after a single concussion. The researchers also found that the concussion group showed less consolidation of negative images and less habituation to negative images. The results were worse for students with multiple concussions. The sleep dependent processes of the brain, now understood to be important to emotional regulation, were not functioning as well in the concussion group, providing an explanation, at least in part, for the persistent mood disorders commonly found after concussion.
Because sleep disruption can have such significant emotional consequences, it must be addressed in treatment following concussion. Key issues in research going forward are the physiological mechanism that causes disruption of sleep following concussion and the best treatment following concussion to improve sleep.