Rest between mild head impacts helps brain recovery, at least in mice, according to a study published Friday.
Georgetown University Medical Center scientists put mice into a special contraption that hit their head with a mechanical piston. The mice’s heads were cushioned and allowed to move during the impact. Scientists found that mice hit in the head weekly recovered better than those hit daily.
“What we’re trying to do is mimic a fairly strong hit to the head, but the kind of hit that doesn’t cause massive structural damage,” said lead researcher Mark Burns. “Which is the kind of hit you’re seeing in sports on a regular basis.”
These kinds of hits have drawn national attention. They’re associated with the development of chronic traumatic encephalopathy, or CTE, in football players, although causal mechanisms are not yet understood.
Burns said that his study’s methods can be used to answer “some of the very basic questions” people have about concussions.
One such question was what effect rest between head impacts has on recovery. Burns found that, in the day following the impact, bridges between neurons, called synapses, withdrew in the mice’s brains. The mice that were given a week to recover regrew their synapses after each hit. But in the mice that were hit every day, the cycle of destruction and regrowth eventually stopped. Their synapses didn’t shrink and grow — they stayed the same.
“This data is very unexpected,” Burns said. He hypothesized that the synapses shrink to protect the neurons from injury after the impact. Following a concussion, the brain starts accumulating chemicals such as calcium, which flow across the synapses into neurons, potentially killing them. But if the synapses withdraw, the calcium can’t reach the neurons.
Mice concussed daily lost this ability to protect themselves — a discovery that may inform our understanding of traumatic brain injury in people.
Burns also found that brain inflammation in these mice persisted up to a year after the last impact. He said that he doesn’t know why the inflammation is there, or what it’s doing, though this could be an area for future research.
Researchers also looked for the telltale signs of CTE — the buildup of tau proteins — in concussed mice. But they didn’t find it.
“We were actually a bit surprised,” said Emmanual Planel, an author on the paper and associate professor of psychiatry and neurosience at Université Laval in Québec. Planel said that other animal studies had found tau accumulations, but those involved more severe injuries.
But the team did find mild cognitive impairment. Mice hit in the head every day had increased anxiety and trouble balancing, but no learning impairments, researchers wrote in the American Journal of Pathology.
Some cautioned against applying all of these findings to humans.
Rodents are “naturally able to recover from injuries a lot easier than humans can,” said Patrick Sweeney, managing director of Charles River’s Discovery Research Services in Finland, a drug research and development company. Sweeney has done work with rodent models of traumatic brain injury before. Overall, though, Sweeney said that the importance of rest between head impacts in this paper was well established.