Concussions aren’t unusual. It’s estimated that up to 3.8 million sports and recreation-related concussions occur each year. That number doesn’t include other accidents such as car crashes or falls that can cause concussion. Though medical providers categorize concussions as a “mild brain injury” because they are not life-threatening, the effects of this kind of knocks on the head can be serious.

Even mild concussions can have long-lasting effects on the brain, researchers at the University of Cambridge have found.

Their results call into question previous assumptions about mild concussions. It’s not unusual for clinicians to assume that nine out of 10 patients who experience a mild concussion will have a full recovery after six months, based on earlier studies. But the UK researchers found that almost half of those with mild concussions experienced long-term symptoms such as fatigue, depression and headaches, as well as cognitive impairment.

Concussion was associated with increased connectivity between the thalamus and the rest of brain. It seemed the thalamus was trying to communicate more as result of the brain injury.

How can medical professionals predict who will have a quick recovery and who will take longer? Well, that’s the challenge. When doctors suspect a concussion, the usual procedure is to provide a brain scan — either an MRI or CT scan. Both of these techniques will reveal issues such as inflammation or bruising on the brain. But even when it appears that there’s no structural damage, some patients’ symptoms continue for long periods after the initial injury.

“Worldwide, we’re seeing an increase in the number of cases of mild traumatic brain injury, particularly from falls in our ageing population and rising numbers of road traffic collisions in low-and middle-income countries,” Emmanuel Stamatakis, from the Department of Clinical Neurosciences and Division of Anaesthesia at the University of Cambridge, said in a press statement.

“At present, we have no clear way of working out which of these patients will have a speedy recovery and which will take longer, and the combination of over-optimistic and imprecise prognoses means that some patients risk not receiving adequate care for their symptoms,” he continued.

To get a clearer picture of the frequency of serious concussions, Stamatakis and his colleagues looked at over 100 fMRI brain scans (functional MRIs) which show how different areas of the brain interact with each other in patients with mild traumatic brain injury and compared them with scans from 76 healthy volunteers.

The results showed that just under 45 percent of patients were still showing brain injury symptoms — most frequently, fatigue, poor concentration and headaches. The researchers identified abnormalities in these patients in a region of the brain known as the thalamus, the area of the brain responsible for integrating all sensory information and relaying the information all around it.

While some concussive symptoms appear right away, others may not show for hours or days after an injury.

It seems counterintuitive, but the researchers discovered that the concussion was associated with increased connectivity between the thalamus and the rest of brain. It seemed the thalamus was trying to communicate more as result of the brain injury. And the greater this type of connectivity, the poorer the prognosis for the patient.

“We might interpret this as the thalamus trying to over-compensate for any anticipated damage, and this appears to be the root of the long-lasting symptoms that patients experience,” Rebecca Woodrow, a PhD student in the Department of Clinical Neuroscience at Cambridge, said in a press statement.

The findings could help practitioners to choose proper treatments for their concussed patients. “We know that there already are drugs that target these brain chemicals so our findings offer hope that in future, not only might we be able to predict a patient’s prognosis, but we may also be able to offer a treatment targeting their particular symptoms,” said Stamatakis.

While some concussive symptoms appear right away, others may not show for hours or days after an injury. If you hurt your head, be on the lookout for these symptoms. If you are experiencing any of them, don’t wait to get in touch with your health care provider.

  • Headache or “pressure” in the head
  • Nausea or vomiting
  • Balance problems or dizziness, or double or blurry vision
  • Being bothered by light or noise
  • Feeling sluggish, hazy, foggy or groggy
  • Confusion, or concentration or memory problems
  • Just not “feeling right,” or “feeling down”

The study is published in the journal Brain.