Jake Paul's boxing career is still in its nascent stage, but the YouTube star has already experienced some of the effects that can afflict more experienced fighters.
Paul said on In Depth With Graham Bensinger (via TMZ Sports) that he has had cognitive problems since entering into the world of professional boxing.
"I notice it in conversations with, like, with my girlfriend or friends, like, not remembering something that I should be able to remember that happened a couple days ago," he said. "... Sometimes in my speech, where, like, every hundredth or two hundredth word, I'll mess up or, like, slur, which I didn't do that before."
The 24-year-old has four professional fights and one exhibition contest under his belt. He's slated for a rematch with former UFC welterweight champion Tyron Woodley on Saturday in Tampa, Florida.
The connection between combat sports and an increased risk of neurological injuries has been known for a long time.
A 2012 study released by the American Academy of Neurology (via CBSNews.com) found "those with more years of fighting experience overall, as well as those participating in more fights per year, were more likely to have lower brain volumes than fighters who had the least experience."
However, fighters with fewer than nine years of experience didn't show the same kind of correlation.
That isn't to say the risk for a younger fighter such as Paul is nonexistent.
Having already fought at the amateur level, actor Mickey Rourke embarked on a pro boxing career in 1991. His last fight was in 1994, which was enough time for him to put a lot of mileage on his body.
"By the time doctors told him he must stop boxing, he was suffering from memory loss, poor balance and needed extensive plastic surgery to reconstruct his battered face," per CNN's Mairi Mackay.
In August, Paul teased what proved to be a short-lived retirement:
Beyond the money he stands to gain—he'll earn a $2 million purse Saturday—Paul probably carries a chip on his shoulder to silence the skeptics who continue to question his boxing skill.
But the Ohio native might have to look at the bigger picture.