Quinpirole-induced sensitization to noisy/sparse periodic input: temporal synchronization as a component of obsessive-compulsive disorder.

Quinpirole-sensitized rats were tested on a discrete-trials 40-s peak-interval procedure using lever pressing as the instrumental response. Although there was no evidence of rhythmical activity in lever pressing, periodic output was observed in a secondary response (food-cup entries) during the inter-trial interval following the delivery of reinforcement on fixed-interval trials, but not during unreinforced probe trials. This repetitive pattern of behavior with a 40-s period points to the primacy of reinforcement as a time marker and an increased tendency to synchronize to noisy and sparse periodic input as a result of reduced inhibitory control in cortico-striatal circuits following chronic quinpirole administration. Parallels between quinpirole-induced rhythmical behavior and the repetitive motor habits frequently observed in obsessive-compulsive disorder are discussed.