Concussion researchers have long suspected that damage to the brain’s corpus callosum could be the underlying reason behind certain side effects of concussion, including dizziness or vision problems.
Their hypothesis states that damage to the corpus callosum — a thick bundle of nerves that connects the brain’s two halves — could affect coordination between these halves, but the theory has been difficult to prove.
Although still not proven, Stanford University researchers offer new evidence to support the idea in a new study. To do this, they combined data from sensors worn by athletes and created model simulations of brain movement. They also reviewed brain images of people with and without concussions.
Their findings, published in the journal Biomechanics and Modeling in Mechanobiology, suggest that impacts to the side of the head might cause harmful vibrations in a structure connected to the corpus callosum.
“Concussion is a big, vague term, and we need to start breaking it down,” said Dr. Fidel Hernandez, a former graduate student in the lab of Dr. David Camarillo, assistant professor of bioengineering at Stanford University, and co-lead author of the paper. “One way we can do that is to study individual structures that would be likely to cause traditional concussion symptoms if they were injured.”
The study involved data from mouth guards worn by football players. Each mouth guard recorded head movement and acceleration in six directions.
After studying 115 impacts recorded by these mouth guards, the team found that two impacts were associated with concussion diagnoses. By applying the mouth guard measurements to a simulation of the neck, head and brain, the researchers saw instances where the corpus callosum was pulled around by a structure above it called the falx.
The falx sits like a mohawk hairstyle between the brain’s two halves and is stiffer than the rest of the brain, like leather versus gelatin. Watching reproductions of the recorded impacts and additional simulations, the team found that hits to the side of the head could produce vibrations in the falx, due to its stiffness.
These vibrations could then move down to the corpus callosum, creating the kind of tissue strain that is often implicated in concussion. Simulated strikes that made the head tilt toward the shoulder produced C-shape waves in the falx, while those that caused the head to turn produced S-shaped waves.
Next, Dr. Michael Zeineh, assistant professor of radiology and his lab team, including former postdoctoral fellow and co-lead author of the paper Dr. Maged Goubran, looked at magnetic resonance imaging (MRI) scans from the two athletes who had been diagnosed with concussion.
The researchers looked with the most sensitive method available — diffusion imaging — and found evidence of possible damage to the corpus callosum in both brains.
Diffusion imaging is rarely used in clinical practice and, even with this advanced technology, the researchers only saw the corpus callosum abnormalities because they knew where to look and had a comparison group: scans from athletes from the same sport and with similar years of experience who had never been diagnosed with concussion.
“The bottom line is, when we do post-concussion brain scans in clinical settings, we don’t find anything. I’d say 95 percent of them are normal,” said Zeineh, who is also co-senior author of the paper. “Clinically, we interpret by eye, but the kinds of changes we’re showing in the paper, you can’t see with your eye. Concussion cannot be diagnosed by imaging alone.”
Since there were only two concussions in the data, the association between side impacts, corpus callosum strain by the falx and concussion is still a hypothesis, say the researchers. A few previous studies have discounted this link but none have combined biometric measurements, simulations and neuroimaging at this resolution.
The researchers need more data to see how their hypothesis holds up and they are already working with women’s lacrosse and additional football players to obtain that.
When someone is diagnosed with a concussion, the treatment is almost always the same. The problem is that there are likely many kinds of concussions with symptoms that depend on which part of the brain was injured and how badly.
“All concussions are not created equal,” said Hernandez. “We try to draw a line — a binary ‘yes concussion’ or ‘no’ — but concussions happen on a gradient.”
Source: Stanford University