This is an old article from 2009. By tinnitus intensity they mean perceived loudness. As the titles says, they measure electric activity in the auditory cortex. They compared it with declarations of patients about the loudness of their tinnitus and found a correlation.
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0007396
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0007396