Sex Dependent Decreases in REM Sleep After TBI and the Impact it May Have on Recovery

Grace Griesbach, PhD

Credit: Centre for Neuro Skills

We spend about a third of our lives sleeping. Thus, it is not surprising that sleep plays a very important role in our overall health. Studies repeatedly show that sleep is important for optimal cognitive processing, endocrine regulation, immune system functioning and emotional well-being. About 14% percent of adults have trouble with sleep. However, the prevalence of sleep disorders largely increases after a traumatic brain injury (TBI). Moreover, the incidence of sleep alterations appears to be independent of TBI severity.

TBI survivors frequently report an array of sleep disorders ranging from hypersomnia to insomnia. Most notable is the disruption of normal sleep cycles after TBI. This is also referred to as fragmented sleep. A typical, sleep cycle lasts from 90 to 110 minutes and consists of 1 REM stage and 3 non-REM stages. The REM stage along with the non-REM stage 3, i.e. deep sleep, are particularly important for cognitive wellbeing. Stages are characterized by specific brain wave activity and are best observed by an overnight polysomnography (PSG) study. PSG studies are also widely utilized for the diagnosis of sleep related disorders.

A recent study, by Stefanie Howell, PhD, CBIS, and me, explored how sleep can influence recovery in patients with chronic TBI. One of the aims of this study was to identify disruptions in sleep cycles while considering sex as a biological variable. It is well known that sleep is influenced by the sex assigned at birth, however there is a notable lack of TBI studies that factor sex as a variable when analyzing sleep’s structural organization. Here, we evaluated medical records from chronic patients with TBI that underwent an overnight PSG.

Findings from this investigation revealed that sex assigned at birth was an important variable when addressing sleep after a TBI. Both men and women had similar total sleep times, however, women had significantly less REM sleep time compared with men. Interestingly, women also had more disability as indicated by the Mayo Portland Adaptability Scale. This scale is widely utilized to assess functional outcome after a brain injury.

Women also reported more cognitive and emotional difficulties. Here we also showed that REM sleep was significantly associated with short-term episodic memory. Individuals that had little REM sleep during the night performed poorly in a verbal memory test compared to those that had more REM sleep.

Another goal of this study was to determine how medications can impact REM sleep. Patients with TBI are frequently taking medications that can affect sleep structure. Melatonin supplement is used to promote sleep and was found to be positively associated with REM. Whereas these findings support the use of melatonin it should be noted that duration of melatonin treatment was not addressed.

In conclusion, findings from this study provide further evidence that sleep fragmentation contributes to chronic morbidity. TBI research can be particularly challenging due to the diversity of TBI survivors. Findings from this study highlight that biological sex provides insight on the pathophysiology of sleep and needs to be considered in future studies.

REFERENCES
1. Griesbach G, Howell S. The Impact of REM Sleep in Memory After a Traumatic Brain Injury (TBI) and the Importance of Considering Sex a Biological Variable. Presented at: 2024 North American Brain Injury Society’s Annual Conference on Brain Injury; March 27-30.

Griesbach is the national director of clinical research for Centre for Neuro Skills and is most well known for her National Institute of Health funded research on TBI that has focused on mechanisms that facilitate recovery and enhance rehabilitation. She is a member of the NIH and Department of Defense Sports Concussion Common Data Elements Working Group. Griesbach currently holds an appointment at the Neurosurgery Department, Geffen School of Medicine, UCLA and is also the vice president elect for the National Neurotrauma Society.