Why do some head knocks result in a concussion while others escape them, despite the similar nature of the impact?
The concept seems simple enough: Taking a hard hit to the head can result in a concussion. But researchers at Stanford University in California report that, in most cases, the connection is anything but simple.
The study team, reporting in the journal Physical Review Letters, found that the key difference between impacts that led to concussions and those that did not had to do with how — and more importantly where — the brain shakes.
Combining data recorded from American football players with computer simulations of the brain, a team working with David Camarillo, an assistant professor of bioengineering, found that concussions and other mild traumatic brain injuries seemed to arise when an area deep inside the brain was shaken more rapidly and intensely than surrounding areas.
But they also found that the mechanical complexity of the brain means there is no straightforward relationship between different bumps, spins and blows to the head and the likelihood of injury.
The findings could ultimately lead to better helmet designs and improve on-the-field diagnostics for athletes following head blows.
“Concussion is a silent epidemic that is affecting millions of people,” said Mehmet Kurt, a former postdoctoral fellow in Camarillo’s lab.
Kurt and Kaveh Laksari, also a former postdoctoral fellow with Camarillo, are co-lead authors on the paper.
Exactly how concussions come about remains something of a mystery.
“What we were trying to do is understand the biomechanics of the brain during an impact,” Kurt said.
Armed with that understanding, engineers could better diagnose, treat and hopefully prevent concussion.
In previous studies, Camarillo’s lab had outfitted 31 college football players with special mouthguards that recorded how players’ heads moved after an impact, including a few cases in which players suffered concussions.
Laksari and Kurt’s idea was to use that data, along with similar data from NFL players, as inputs to a computer model of the brain. That way, they could try to infer what happened in the brain that led to a concussion.
In particular, they could go beyond relatively simple models that focused on just one or two parameters, such as the maximum head acceleration during an impact.
It was this work that led to the researchers identifying the key difference between impacts that led to concussions and those that did not.
After an average hit, the researchers’ computer model suggests the brain shakes back and forth around 30 times a second in a fairly uniform way – that is, most parts of the brain move in unison.
In injury cases, the brain’s motion is more complex.
Instead of the brain moving largely in unison, an area deep in the brain called the corpus callosum, which connects the left and right halves of the brain, shakes more rapidly than the surrounding areas, placing significant strain on those tissues.
Concussion simulations that point to the corpus callosum are consistent with observations — patients with concussions do often have damage in the corpus callosum.
However, Laksari and Kurt emphasize that their findings are predictions that need to be tested more extensively in the lab, perhaps even using human brains that have been donated for scientific study.
“Observing this in experiments is going to be very challenging, but that would be an important next step,” Laksari said.
Perhaps as important as physical experiments are additional simulations to clarify the relationship between head impacts and the motion of the brain – in particular, what kinds of impacts give rise to the complex motion that appears to be responsible for concussions and other mild traumatic brain injuries.
Based on the studies they have done so far, Laksari said, they know only that the relationship is highly complex.
Still, the payoff to uncovering that relationship could be enormous.
If scientists better understand how the brain moves after an impact and what movement causes the most damage, Kurt said, “we can design better helmets, we can devise technologies that can do onsite diagnostics.” This, in turn, could lead to important sideline diagnostic calls in real time, which could improve outcomes for those who take a nasty hit to the head.
The study was supported by the Child Health Research Institute, the Lucile Packard Foundation for Children’s Health, Stanford’s Clinical and Translational Science Award and the Thrasher Research Foundation.