Orig. Post June 9, 2015 by Charles Q Choi, Braindecoder | Re-Post June 23, 2015
It could be a blow to the head on a football field. A strong jolt as a speeding car comes to a halt. A blast wave from an explosion a few yards away. The force of the blow can shake the brain inside the skull, smashing it against the inner walls of its vault. The result is a traumatic brain injury, a diagnosis that more than 2 million Americans receive each year.
The most common type of a traumatic brain injury is concussion. But despite its prevalence, pinpointing what goes wrong inside the head in concussion is actually quite difficult. One reason for that is that researchers have problems defining what concussion even is. “There are 43 different definitions of what a concussion is right now,” said neurosurgeon Uzma Samadani, co-director of the NYU Cohen Veterans Center.
From the outside, a concussion involves headaches, nausea, confusion, blurry vision, and problems with concentration, memory, balance, coordination, energy and mood. But what happens during a concussion inside the brain at the cellular level can be extraordinarily complex, and is not even entirely understood by science.
Jolted brain tissue and torn connections
One probable cause of many symptoms of concussion is known as cortical spreading depression, in which proteins known as ion channels on the surfaces of brain cells essentially get stuck in what is either their on or off position, letting ions into or out of the cells when they should not. Cortical spreading depression can lead to headache, decreased cognitive function, and seizures. “This is a very serious problem that gets worse over time — it actually spreads,” Samadani said. “It’s not easily fixable, but there are medications that can change ion channel function.”
Another possible cause of symptoms is how the delicate neurons bridging the pituitary gland with the brain’s hypothalamus region can get damaged when the head simultaneously rolls and snaps forward, similar to what happens in whiplash. This can lead to hormonal problems. “Months afterward, people can feel horrible, feel depressed, have problems with memory, and experience changes in personality,” Samadani said. “They can have a lot of problems with daily functions.”
A concussion can also involve microhemorrhages — that is, microscopic bleeding in the brain. As iron in the blood from this bleeding breaks down, it can be toxic to neurons, resulting in movement disorders and cognitive problems.
Microhemorrhages may be accompanied by stretching or tearing of neurons. “This results in impaired connections between different parts of the brain,” Samadani said. The resulting symptoms depend on where the injury happened in the brain. “That’s the thing about concussions — they’re all different depending in part on where one gets hit on the head.”
Confusing symptoms
Even without a blow to the head, a person could experience concussion symptoms that are caused by oxygen deprivation to the brain. “For example, imagine a person who is hit by a bus and falls to the ground. They may not even hit their head, but they may suffer other injuries such as a fracture to their femur that causes blood pressure to drop so severely that they may lose consciousness and not have enough oxygen reaching their brain,” Samadani said. “This is another way to get damage distributed across the brain, and particularly in areas vulnerable to lack of oxygen. After the trauma, a person may say they don’t feel the same — for instance, that their memory’s gone.”
A number of concussion symptoms may not be due to brain damage — they could result from a neck muscle spasm, or a scalp injury, or bone pain from the skull, or an inner ear problem, Samadani explained. “In fact, our research suggests that the vast majority of people who are hit in the head and have some concussion symptoms actually do not have brain damage per se,” Samadani said. “Often these are people who recover more quickly, depending on where their injuries are.”
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Injuries that do not involve brain damage can still be problems, Samadani said. The muscle strain from neck spasms can lead to major headaches; inner ear problems can lead to problems with balance and dizziness; and scalp pain can be severe enough to cause vomiting, she explained.
“You can have a person who is hit in the head and has a headache, who actually has any of a myriad of problems wrong with them, many of which can cause the same symptoms,” Samadani said. “To further complicate the problem, many people have more than one of these problems at the same time.”
Improving the technology to detect concussions
The lack of a definitive definition of concussion means that it is difficult to diagnose it for sure or even calculate how often it happens. One estimate is that between 4 million and 7 million people per year get CT scans for concussion, Samadani said. However, CT scans and MRIs often miss concussions, she noted.
Numerous research programs, including some supported by the National Institutes of Health and the National Football League, are working to enhance the methods and technologies used for detecting concussions. Samadani and her colleagues are currently working on way to diagnose concussion using eye-tracking technology. Current estimates from optometrists suggest that up to 90 percent of patients with concussions have problems with eye movements — the injuries that lead to concussions may often damage circuits in the brain stem that coordinate eye movements.
In experiments, the researchers have compared healthy volunteers with patients who visited emergency rooms with head trauma, tracking the eye movements of participants as they watched music videos such as Shakira’s “Waka Waka” or “Under the Sea” from Disney’s “The Little Mermaid.” As the videos played, they moved slowly clockwise around the outer edge of the screen.
When people have concussions, both eyes may try to track movements, but one eye might undershoot or overshoot in a particular direction, Samadani said. The less coordinated the eye movements of trauma patients were, the more severe their concussive symptoms were. Samadani has submitted patents describing this technology that are owned by NYU and the U.S. Department of Veterans Affairs and are licensed to Oculogica, a company co-founded by Samadani and co-investigator Robert Ritlop.
“I think it is extremely important to be able to detect and quantify concussion because without objectively being able to do that, we cannot begin to treat the problem,” Samadani said. “Right now we still have people who get hit in the head and have problems for months and even years and we don’t see a problem on conventional radiographic imaging so they are not getting treated. People’s lives can be ruined socially and economically because they can have a lasting problem that impairs their functioning. While most people who are hit in the head will recover very quickly, we need to be able to identify and help those who do not.”