Harrison (concussion) was a limited participant in Thursday's practice, Brooke Pryor of ESPN.com reports.
Harrison suffered a concussion last Sunday against the Ravens, exiting the game in the second quarter and failing to return. The inside linebacker took his first step to clearing the league's concussion protocol Thursday by logging a limited practice. He will have two more chances to be cleared by an independent neurologist and upgrade to full practice before the Steelers' showdown with the Dolphins on Monday night.