Even a mild concussion can have lasting effects on the brain, according to researchers at the University of Cambridge in Engalnd. Using data from a study across Europe, the team has found that almost half of people who experience a head injury show changes in how different parts of the brain communicate with each other, potentially leading to long-term symptoms such as fatigue and cognitive impairment.

Concussion, which is a result of a blow or jolt to the head, can happen from falls, sports injuries, cycling accidents, car crashes, and other similar incidents. Despite being called “mild,“ it is often associated with persistent symptoms and incomplete recovery, including depression, cognitive impairment, headaches, and fatigue.

While some recent studies suggest that nine out of 10 people who experience a concussion will fully recover within six months, emerging evidence indicates that only half of them achieve full recovery. This means that a significant portion of patients may not receive adequate care after their injury.

Predicting which patients will recover quickly and who will take longer to recover is challenging. Currently, patients suspected of having a concussion typically undergo a brain scan, such as a CT scan or an MRI scan, which look for structural problems like inflammation or bruising. However, even if these scans do not show obvious structural damage, patients’ symptoms may persist.

Emmanuel Stamatakis, PhD, MSc, BSc, from the University of Cambridge’s department of clinical neurosciences and anesthesia division, says: “We are seeing an increase in the number of cases of mild traumatic brain injury worldwide, particularly from falls in our aging population and rising numbers of road traffic collisions in low- and middle-income countries. At present, we have no clear way of determining which of these patients will recover quickly and which will take longer, and the combination of overly optimistic and imprecise prognoses means that some patients risk not receiving adequate care for their symptoms.“

Stamatakis and his colleagues studied functional MRI (fMRI) brain scans, which show how different areas of the brain coordinate with each other, from 108 patients with mild traumatic brain injury and compared them with scans from 76 healthy volunteers. The patients were also assessed for ongoing symptoms.

In the results published in the journal Brain, the team found that just under half (45%) of the patients were still experiencing symptoms resulting from their brain injury, with the most common symptoms being fatigue, poor concentration, and headaches. The researchers discovered that these patients had abnormalities in a region of the brain called the thalamus, which integrates sensory information and relays it around the brain. 

Interestingly, concussion was associated with increased connectivity between the thalamus and the rest of the brain, meaning the thalamus was trying to communicate more due to the injury. The greater the connectivity, the worse the prognosis for the patient.

Rebecca Woodrow, a PhD student at the University of Cambridge, explains: “Despite there being no obvious structural damage to the brain in routine scans, we saw clear evidence that the thalamus—the brain’s relay system—was hyperconnected. We might interpret this as the thalamus trying to overcompensate for any anticipated damage, and this appears to be at the root of some of the long-lasting symptoms that patients experience.“

By studying additional data from PET scans, which can measure the chemical composition of body tissues, the researchers were able to make associations with key neurotransmitters depending on the long-term symptoms a patient displayed. For example, patients experiencing cognitive problems such as memory difficulties showed increased connectivity between the thalamus and areas of the brain rich in the neurotransmitter noradrenaline; patients experiencing emotional symptoms, such as depression or irritability, showed greater connectivity with areas of the brain rich in serotonin.

Stamatakis adds: “We know that there already 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.”