The NFL and college football have come under fire in recent years due to the mounting scientific evidence that shows the damage that can be caused by simply playing the game. Everyone knows that concussions are bad, but repeated impacts to the head that aren’t severe enough to cause a concussion can be serious as well, and a new study shows that even a single season can significantly alter brain matter.

The study, which was published in Science Advances, was conducted by researchers at the University of Rochester who tracked the brain health of nearly 40 of the school’s football players. Equipped with special helmets to monitor impacts, the data shows dramatic changes in the brain even when players can avoid serious concussions.

The researchers took MRI scans of each player’s brain before the season started and then revisited the MRI when players were done for the year. They monitored the various areas of the brain including the “midbrain” which is important for a number of vital functions including hearing.

The team discovered that, likely due to the central location of the midbrain within the skull, it’s more likely to be affected by blows to the head, regardless of the angle of impact.

When the results from before and after the season were compared, the researchers discovered noticeable changes for over two-thirds of the players in the white matter of the brain, especially in the midbrain region. This is despite the fact that only two of the players being monitored had been diagnosed with a concussion at any point in the season.

Chronic traumatic encephalopathy, or CTE, has been implicated in the deaths and mental decline of a number of NFL veterans, and the condition has been linked to everything from severe depression to dementia. Understanding what kinds of impacts can contribute to a person developing CTE is incredibly important for the health of the players (as well as the sport), but this study seems to indicate that damage to the brain can be seen even after a single season of play.