The link between concussions and depression has been in the news a lot lately, most notably with several high-profile suicides among college and high-school football players. While researchers have little doubt that concussions can lead to depression and anxiety, what underlies that connection hasn't been entirely clear. Now, researchers report they've found a clue: The injuries that lead to depression and anxiety may damage neural signal carriers deep inside the brain.
Several million people sustain traumatic brain injuries (TBI) in the United States every year—2.5 million in 2010, according to the Centers for Disease Control and Prevention—which range from a bump that briefly disrupts brain function to something much, much worse. Psychologists know some of those injuries lead to depression and anxiety, but they don't have a basic estimate of how many people with a TBI develop mental health issues; depending on who you ask, the number is anywhere from 15 to 70 percent.
Researchers understand nearly the same amount—which is to say, very little—about why TBI leads to depression, and that's especially true for concussions and other mild TBI. For example, routine MRI brain scans after a mild head injury usually don't turn up anything abnormal, suggesting that a brain injury itself might not directly cause subsequent psychiatric disorders at all.
White matter in patients with depression after a mild TBI was in worse shape compared to the 29 patients in the control group.
Not so fast, argue Lea Alhilali and colleagues at the University of Pittsburgh Medical Center. MRI can tell you a lot about the brain, but it's well known they don't pick up on everything. In particular, axons—the parts of brain cells responsible for passing signals from one cell to the next, also known as white matter—are invisible to conventional MRI. That's kind of a problem for people studying brain injury and depression or anxiety, as there's a fair amount of evidence that damaged axons lead to depression.
To study the role damaged axons might play in post-mild TBI depression and anxiety, Alhilali examined brain scans from 74 patients who'd previously been seen for mild TBI and been evaluated using diffusion tensor imaging, a specialized MRI technique used to measure white matter integrity. Of those, 32 were depressed and 18 had anxiety, while 29 had no psychiatric problems. (The numbers don't add to 74; some patients had multiple neuropsychiatric issues.)
White matter in patients with depression after a mild TBI was in worse shape compared to the 29 patients in the control group, the team found, particularly in the nucleus accumbens and two other brain regions that past research has linked to depression. Conversely, white matter in the cerebellar vermis is a region that some studies suggest plays a role in fear of learning—though it's not a region usually associated with anxiety in patients without a brain injury.
The team writes that their study does have limitations—it relied on a relatively small sample of people, all of whom had come to the hospital following brain trauma—but that the results could help psychiatrists better decide how to treat patients with TBI in the future.
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