Studying the effects of multiple concussions

By William P. Meehan III, MD, director of the Micheli Center for Sports Injury Prevention, director of the Sports Concussion Clinic and director of Research for the Brain Injury Center at Children’s Hospital Boston. His research has been funded by the National Institutes of Health, the National Football League and the Center for the Integration of Medicine and Innovative Technology. Meehan is author of the book Kids, Sports, and Concussion: A Guide for Coaches and Parents

On June 6, 2011, the Boston Bruins were playing the Vancouver Canucks in game 3 of the Stanley Cup finals. Bruins forward Nathan Horton had passed the puck to his teammate Milan Lucic when he was blindsided by the Canucks’s Aaron Rome, who buried his left shoulder into Horton’s face. Horton’s head was spun backwards, down towards the ice. The back of his head was the first part of his body to make contact with the ice. He was knocked unconscious. His arms became rigid. His eyes rolled back in his head. He had a convulsion.

Nathan Horton was concussed.

Concussion is all too common in sports, particularly those, like ice hockey, that involve body-to-body collisions. Yet it’s still somewhat of a medical mystery. Until the last 10 to 15 years, most medical professionals didn’t think concussions posed enough risk to warrant much research. Thus, we know very little about it today.

Although the signs and symptoms of a concussion can be serious, as seen in the case of Nathan Horton, it can be hard to see them when you look at images of concussed brains; CT scans and MRIs often don’t clearly show how a concussed brain has been injured. There’s no bruising, no bleeding and no swelling.

Meehan and colleagues modeled the effects of concussion in mice, having them navigate the classic Morris water maze to measure changes in memory and learning. (This image, from Wikimedia Commons, shows a rat.)

To better understand how these types of injuries affect brains, I set out with Rebekah Mannix, MD, MPH at Boston Children’s Hospital and Michael Whalen, MD, PhD of Massachusetts General Hospital, to develop a mouse model of concussion. The research was paid for by a grant from the National Football League (NFL).

It was a difficult task. The mice needed to have measurable signs of concussion (poor memory, difficulty learning, loss of consciousness or convulsions), but not a structural brain injury (bleeding, swelling or bruising of the brain).

Once we had our model, we used it to determine whether the effects of concussions are cumulative, which means they get worse the more you have. Some athletes who sustain multiple concussions during their careers report problems later in life, like poor memory, slow reaction time, slowed thinking and difficulty learning. But despite these issues, the athletes’ brain scans often look normal, leading some people to question whether anything is truly wrong with them. Some people even accuse them of “malingering” — trying to avoid work, collect disability payments or sue the NFL because of their condition. Others theorize that these athletes’ problems aren’t due to concussions, but from steroid use, alcohol abuse, depression or drugs.

But mice don’t malinger, use steroids or engage in substance abuse, making our mouse model of concussion perfect for testing whether repeated concussions can really cause problems with memory and learning.

Dr. Meehan and the Stanley Cup

Based on our research, we’ve seen that repeated concussions can lead to learning and memory problems. But not only does our model strongly suggests that multiple, mild concussions affect a brain’s ability to function normally, it also indicates that the amount of time needed to fully recover from a concussion in order to avoid future problems could be longer than many people realize.

The lesson here is that the current practice of removing concussed athletes from play–allowing them enough time to recover before risking additional injuries–may protect brain function in the short-term, but may be less effective at preventing the long-term, cumulative effects of repeat concussions.

While we still need to know more about the effects of repeated concussions, especially for young athletes, some things are certain.

The effects are cumulative.

The consequences are real.