Sensorimotor gating is a neural mechanism that filters out extra stimuli and processes information that comes in rapid succession. Prepulse inhibition (PPI) is a form of startle plasticity that provides an operational measure of sensorimotor gating. Sensorimotor gating and PPI may be modulated by serotonin transporters (5-HTT), and deficits in this function are observed in obsessive compulsive disorder (OCD) and autism. Evidence has shown that reducing serotonin transporters leads to improvement in perseverative (repetitive) behaviors. This study will use behavioral and genetic mouse models to identify the neural mechanisms by which serotonin transporters (5-HTT) control sensorimotor gating deficits and repetitive behaviors. This approach could lead to novel animal models of the sensorimotor gating deficits and perseverative behaviors in OCD and autism.