Teens and young adults who have symptoms of post-concussion syndrome after multiple concussions may have disrupted connectivity in the brain’s default-mode network, a study shows.

The findings suggest there may be a number of concussions beyond which it is unsafe to continue playing contact sport, the researchers say.

The US study, presented at the Radiological Society of North America annual meeting, examined 142 young people with concussion (67 female, mean age 18) with a history of clinically diagnosed mild traumatic brain injury and post-concussion syndrome.

Participants, together with 27 age- and sex-matched controls without concussion (12 female, mean age 21) underwent resting-state functional MRI (fMRI).