It has been shown these last years that optogenetic tool, that uses a combination of optics and genetics technics to control neuronal activity with light on behaving animals, allows to establish causal relationship between brain activity and normal or pathological behaviors [3]. In combination with animal model of neuropsychiatric disorder, optogenetic could help to identify deficient circuitry in numerous pathologies by exploring functional connectivity, with a specificity never reached before, while observing behavioral and/or physiological correlates. To illustrate the promising potential of these tools for the understanding of psychiatric diseases, we will present our recent study where we used optogenetic to block abnormal repetitive behavior in a mutant mouse model of obsessive-compulsive disorder [1]. Using a delay-conditioning task we showed that these mutant mouse model had a deficit in response inhibition that lead to repetitive behaviour. With optogenetic, we could stimulate a specific circuitry in the brain that connect the orbitofrontal cortex with the basal ganglia; a circuitry that has been shown to be dysfunctional in compulsive behaviors. We observed that these optogenetic stimulations, through their effect on inhibitory neurons of the basal ganglia, could restore the behavioral response inhibition and alleviate the compulsive behavior. These findings raise promising potential for the design of targeted deep brain stimulation therapy for disorders involving excessive repetitive behavior and/or for the optimization of already existing stimulation protocol [2].