Barnes is recovering from a concussion and has apparently made it far enough through the concussion protocol to be cleared to go full participation. Of course, he didn't actually go through a full practice Thursday because the Rams do not practice on Thursdays.
Because the league requires teams to send in an injury report on Wednesday, Thursday and Friday, the Rams' Thursday injury report is hypothetical. In other words, had the Rams practiced Thursday, the team estimates Barnes would have been full participation.
Barnes' upgrade was the only change to the Rams' injury report from Wednesday to Thursday.
Here's the full report:
Full participation: Barnes (concussion), DE Chris Long (knee).