Dopamine and serotonin are two brain-wide acting neurotransmitters involved in a variety of behaviours including learning, motivation and impulse control. Moreover, these two neuromodulators are the main targets of pharmacological treatments for disorders such as obsessive-compulsive disorder (OCD), addiction, and attention deficit hyperactivity disorder (ADHD). Despite their important roles in health and disease, no clear consensus has been reached on how exactly these two neurotransmitters influence behaviour. In this project, led by Isis Alonso-Lozares, we aim to disentangle this by using fiber-photometry and fluorescent genetically encoded sensors to monitor striatal serotonin and dopamine transmission in different behavioural paradigms.