The objective of this project is to demonstrate the inhibition of human brain PDE4 by HT-0712, by measuring the inhibition of [11C]R-rolipram binding, a radiotracer which also binds to and inhibits PDE4. Plasma samples will be drawn to determine if there is a relationship between plasma pharmacokinetics of HT-0712 and its pharmacodynamic effect, as determined through the inhibition of [11C]R-rolipram binding in the brain.