Understanding the Nuances of Shearing Injuries in the Brain
So if you're trying to think of a performance test, you can just do reaction times, add them up, and look at variability. The problem is if you get a reaction time every couple of seconds and you add it up, you're looking at 20 to 30 minutes of reaction times to get some kind of performance variability index. So we switched to eye movements. We're looking at circular smooth pursuit, which is just look at a dot going around in a circle. It's a continuous task, so it's not discontinuous--continuous task. I see how well your eyes synchronize with the dot going around. I have cameras looking at your eyes. I can see how well you're looking at that dot and predicting where it's going to be. And indeed, we see in patients that have recent traumatic brain injury or persistent traumatic brain injury--we're talking about concussion. People that have acute concussion or persistent concussion symptoms have variability. In other words, you see this kind of wobble of their eyes where they're really not predicting well. So it's like the ball is coming and their hand is swinging several times trying to figure out when the ball is going to come. You see the same thing in eye movements, sort of this wobble. And so we formed a consortium back in 2002 with UC San Francisco-- Geoff Manley out there and Pratik Mukherjee, who is a neuroradiologist, Rich Ivry--and people here at Cornell. The hypothesis was that people coming in with acute concussion would have timing problems and that it was as a result of shearing injury in their brain and this would be picked up with diffusion tensor imaging. Pratik Mukherjee at UCSF is an expert in this area, and so we did MRIs on these subjects and we did timing tests, cognitive tests, and then we followed them from the emergency room out to 1 month, 3 months, and out to 1 year. There's a publication about to come out on this, and we've published other articles about this group of patients, both acute and people with persistent concussive symptoms. It looks like these subjects that the frontal white matter tracts that are involved in attention are the most vulnerable tracts that we see in mild traumatic brain injury. And the reason for that is probably because they are up front. And when you have a concussion, the head moves around. The problem, by the way, is not the focal impact to the head; it's the neck. The neck is moving, and you get this rapid whiplash of the brain. And because the frontal lobes are so far away from the back of the head where the neck is, they get subjected to the most shearing force. And so these areas in the front part are the most vulnerable, and that's what we see on diffusion tensor imaging. That's where we see these kind of shear injuries. And this makes perfect sense because when you're paying attention, this is where the attention circuit is. It's the dorsolateral prefrontal cortex connected to the parietal lobe and also the cerebellum. These circuits are involved in paying attention. When you get this sort of rapid whiplash and shear these tracts you get these attention problems, which is what you see in concussion. So we're trying to build a scientific foundation for what is really happening in concussion and what kind of symptoms and cognitive deficits these patients have as a result of these injuries.
Shearing is the stretching and tearing of the tiny nerve cells that comprise the brain. Learn more about the research and neuroimgaging that shearing can cause when the brain is injured.
See more of Dr. Ghajar's videos here.
Posted on BrainLine February 9, 2012.
Produced by Noel Gunther and Justin Rhodes, BrainLine.