Reminds me of The Terminal Man, especially the line:

"I would assume that extended use would cause you to slowly condition yourself to keep your brainwaves at a low frequency, probably impeding concentration and cognition."

Of course, The Terminal Man had the opposite set-up: when he became agitated, his pleasure center was stimulated, and he calmed down again. This conditioned his brain to become agitated again, so it got another injection of pleasure, until he was constantly agitated/pleasured.