Which StarTrek episode is this?

there was an episode with Reginald Barclay in which Barclay goes to the holodeck and has the computer assemble piece by piece a "brain interface" or something. At one point he has to tell the computer how to create a new piece of equipment to make it work. But once it's all together he sits in the chair and takes control of the enterprise, and runs it all with his brain. (I think his brain was super-sized at the time somehow, but I forget.)

Anyone know what episode that was?