Fractured sleep worsens outcomes after TBI, study finds

Fragmented sleep worsens recovery after traumatic brain injury (TBI), causing loss of REM sleep and greater fatigue in injured mice, a study has found.

REM (rapid-eye-movement) sleep helps the brain consolidate new information and supports concentration and mood. Losing REM can impair brain and cellular function.

The researchers found that mice without a head injury could make up for some REM loss caused by interruptions, but injured mice could not.

Olga Kokiko-Cochran, senior author and associate professor of neuroscience in the College of Medicine at Ohio State, said: “I think sleep has gone underappreciated as a key determinant of traumatic brain injury outcomes for a long time.”

“A brain injury doesn’t occur in isolation.

“We have to think about the recovery environment and acknowledge that there are effects of external stimuli.

“We set up the paper to think about recovery in a hospital, rehabilitation or even a home setting where there are lots of things in the environment that might influence someone’s sleep, and oftentimes those may go unrecognised or unnoticed or even downplayed as to how important they could be in influencing recovery.”

The experiments involved four groups of mice: those with a moderate TBI exposed to either sleep fragmentation or no disturbance, and mice that had surgery but no brain injury that received either normal or fragmented sleep.

The injuries resembled the type of TBI that could result from a fall, the most common cause of traumatic brain injury.

Select mice from each group were implanted with sensors to detect brain and muscle activity, body temperature and cage activity for 30 days after surgery or injury.

Sleep was interrupted by a bar that swept across the floor of the mouse cage every two minutes during the first four hours of the animals’ sleep phase, intended to mimic a period when sleep need is high, such as when a patient might struggle to fall asleep in a clinical setting.

Results showed that after about a week, mice with TBI were less active than uninjured mice, and their activity continued to decrease over weeks three and four.

While sleep fragmentation alone brought on fatigue, interrupted sleep on top of the TBI significantly intensified it.

Christopher Cotter, co-first author of the paper and student in Ohio State’s Neuroscience Graduate Program, said: “So the sham mice are compensating for the loss, but all of the animals with TBI are not compensating for that loss and they continue not compensating for the loss over the four weeks.

“They just lose that REM sleep and they don’t get it back.

“We looked to see if they were sleeping more when they were not supposed to be, and the answer was no. So they just lost that sleep, and that was a really striking finding.”

The researchers found that changes in sleep quality occurred primarily between one and 14 days after injury.

Kokiko-Cochran said: “This model of brain injury and sleep fragmentation gives us an opportunity to study things like fatigue, something understudied in the space of traumatic brain injury that can be difficult to model.

“It’s important because many survivors have an opportunity for extended lifespans. They’re surviving sometimes decades after their brain injury, but there are still persistent symptoms.

“We are trying to be conscious of the fact that people are having lots of other experiences that could influence their recovery.”