BLOG: Post-concussion coping mechanism may predict long-term symptoms
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One of the challenges in diagnosing and managing mild traumatic brain injury is that common structural imaging techniques, such as computerized tomography or magnetic resonance imaging, typically don’t show any visible damage to the brain.
This has contributed historically to the perception that mTBI is not a serious condition and that prolonged symptoms are imagined or psychiatric in nature.
My colleagues and I analyzed structural and functional imaging data from the Collaborative European NeuroTrauma Effectiveness Research in TBI (CENTER-TBI) project to measure changes in a specific region of the brain, the thalamus, in 108 mTBI patients and 76 uninjured, healthy control subjects.
The thalamus is a structure in the center of the brain that serves as a kind of sensory relay station, conveying information from sight, sounds and touch to other areas of the brain responsible for processing and interpreting those sensory inputs. It sends visual inputs from the optic nerve to the visual cortex, for example. Beyond its sensory role, the thalamus is important in a host of other functions, including concentration, memory, sleep-wake cycles, learning and decision-making — all functions known to be disrupted by mTBI. From a brain injury perspective, the thalamus is also interesting because its central location means that it absorbs a great deal of force during a head impact, regardless of whether the hit to the head comes from the front, back or side.
For our study, we looked at data only from patients who had no significant risk factors for poor outcomes, so no CT abnormalities, no history of concussion and no neuropsychiatric disorders. Despite the mild nature of their injuries and the lack of risk factors that predict slower recovery, nearly half the mTBI patients (47%) were not fully recovered 6 months after their injury. Fatigue and poor concentration were among the most common long-term symptoms.
One factor that predicted which patients would have prolonged symptoms was thalamic connectivity, which can be detected on functional MRI (fMRI). The mTBI patients — regardless of recovery trajectory — had some degree of increased connectivity in the thalamus compared to healthy controls who did not suffer a mTBI. This acute response is likely beneficial: The new connections help compensate for connections that are lost or damaged due to the injury. However, a very high rate of increased connectivity initially, followed by a drop-off later on, is associated with ongoing post-concussive symptoms. In these cases, it may be that there is significant functional damage. In attempting to compensate, the thalamus may go into “overdrive” and become fatigued, further disrupting many of its normal functions.
It is very compelling to learn that chronic symptoms can have a basis in early thalamic pathophysiology. This lends further support to the idea that patients can still have a very serious injury even though it doesn't show up on a CT or MRI scan, and that there may be better ways to predict who is at risk of delayed recovery. If fMRI continues to demonstrate good prognostic value, it may be worth investing more in this tool for clinical use, or combining fMRI with positron emission tomography scans, which can identify neurotransmitter chemicals such as dopamine and serotonin in the brain. Further work in this area may point to new drug targets and advance other areas of neuroscience to better support patients with mTBI.
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Rebecca E. Woodrow, MSc, holds a Master of Science in cognitive neuroscience and has extensive experience in multimodal neuroimaging and data science. She is a PhD candidate at the University of Cambridge in Cambridge, England, where her research focuses on using big data to better understand the neural consequences of mild traumatic brain injury.
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