Around 56 million people globally suffer a concussion each year. It’s common for concussion to cause short-term symptoms such as a headache, nausea, sensitivity to light and problems concentrating.
But many people also struggle with long-term symptoms – including fatigue, trouble sleeping and concentrating, and emotional distress. Previous research found that clinicians estimated one in ten people might experience long-term symptoms after a concussion.
But our recent study estimates that post-concussive symptoms are far more common. Our study, published in Brain, found that almost half of people who suffered a concussion had not fully recovered six months after their injury.
To conduct our study, we analysed brain scans from over 100 patients who had recently experienced concussion from all across Europe. These brain scans were conducted using a technique called resting-state functional MRI (fMRI).
A resting-state fMRI measures brain activity when a person is at rest, which can be used to understand how different regions of the brain communicate. This allows us to understand if the brain is functioning as it should or if there are problems with a person’s brain connectivity.
A resting-state fMRI can also tell us more than a CT scan or MRI might. While these types of scans are often given to concussion patients, both only look for structural changes in the brain – such as inflammation or bruising.
Such changes often don’t occur in mild concussion cases soon after injury, which may lead clinicians to believe no brain damage has occurred. But a resting-state fMRI can show us more subtle changes in brain function – and may help us better predict who is more likely to develop long-term symptoms.
In our analyses, we specifically looked for changes in a region in the centre of the brain called the thalamus. This region is important in integrating sensory information and relaying it throughout the entire brain.
The thalamus is also thought to be very vulnerable to the kind of external force that leads to concussion (such as a fall or blow to the head).
Our research found that concussion was associated with increased functional connectivity between the thalamus and the rest of the brain very shortly after injury, when compared to 76 healthy control subjects.
In other words, the thalamus was trying to communicate more as a result of the injury. This was despite routine MRI and CT imaging showing no structural changes in the brain.
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While many of us would assume that more connectivity in the brain is a good thing, research looking at more severe head injuries indicates that greater connectivity between brain regions might actually be a sign of the brain trying to compensate and offset damage across the brain.
We also found that almost half of people with concussion had not fully recovered six months after the injury. Our analysis showed that participants who had signs of greater thalamus connectivity in their brain very soon after injury were more likely to later develop post-concussive symptoms, such as fatigue and poor concentration.
Concussion treatment
Our research makes an important step in understanding concussion, showing that even a single brain injury can have clear consequences in some people. This damage may also not show up in the types of scans concussion patients are routinely given, suggesting it may be time to expand the types of imaging used.
We found that in people who experienced long-term symptoms, functional changes were still present in the brain 12 months after the injury. These effects were found in a sub-group who returned for scanning a year after their injury, and were not seen in patients without long-term symptoms.
Concussion is often viewed as a short-term event, but these findings suggest it can be a long-term disease, and some people may take longer to recover than others.
Our study also found that the long-term symptoms a person experiences may relate to different areas of the brain. We found that people who experienced long-term cognitive symptoms (such as concentration and memory problems) had increased connectivity from the thalamus to areas of the brain linked with noradrenaline – a chemical messenger in the brain.
Whereas people who experienced long-term emotional problems (such as depression or irritability) had greater connectivity to areas that produced a different chemical messenger, serotonin.
This not only shows us how concussion affects people differently, it may also give us targets we can use to develop drugs that alleviate concussion symptoms.
While concussion is considered a “mild” traumatic brain injury, our findings show it’s anything but – and can have long-term consequences for a large proportion of people. Although there’s still a lot we don’t know about concussion – including the effects that repetitive concussion may have on the brain – it’s promising to see this condition is being taken more seriously, especially in sports where it can be common.
New UK guidelines for grassroots sports like football and rugby now require players to sit out of play for at least 24 hours after a suspected concussion, which may help to prevent concussion and improve recovery after one.
Rebecca Woodrow receives funding from the Medical Research Council and the Pinsent Darwin Trust.
David Menon receives research funding from the National Institute for Health Research, UK; UK Research and Innovation (UKRI); the Medical Research Council (UK); the Canadian Institute for Advanced Research (CIFAR); Addenbrooke’s Charitable Trust; the Brain Research Trust (UK). He has consultancy or research collaboration agreements with NeuroTrauma Sciences LLC, Gryphon Inc, GlaxoSmithKline Ltd; Lantmannen AB; Pressure Neuro Ltd; Integra NeuroSciences Ltd; Cortirio Ltd; and Calico LLC.
Emmanuel A Stamatakis receives funding from the Canadian Institute for Advanced Research and the Stephen Erskine Fellowship, Queens’ College, University of Cambridge.
