Cognition depend on the cooperation and communication between functionally connected brain areas. Oscillation and synchrony appear to be crucial for the engagement and disengagement of functional neural circuits. Many studies suggest inhibitory neurons in the brain dictates how and when the information is relayed between neuronal ensembles. The valence of these excitation-inhibition interactions are further regulated by neuromodulators such as dopamine (DA) and the diversity of differential expression of different types of neuromodulator receptors. Here, we propose to: 1) invent novel solutions to combine optical stimulation and neurophysiological recordings into one integrated probe drive for implantation in rodents; 2) provide causal evidence that prefrontal (mPFC) parvalbumin-containing (PV) inhibitory neurons are responsible for coordinating prefrontal-hippocampal (mPFC-HPC) oscillation and synchrony and; 3) examine the role of dopamine action on mPFC-HPC interactions and elucidate the specific role of DA receptor subtype-1 in PV neurons in coordinating DA-mediated effects. The goals of the proposed project will be achieved by using a fully multidisciplinary approach combining state-of-the-art molecular, neurophysiological, genetic and behavioural techniques. Particularly, innovative use of optogenetic tools will be used to control neural activity and RNA interference will be used to knock-down dopamine receptor expression by the use of viral vectors and transgenic animals. We expect to be able to provide novel solutions to simultaneously apply optical stimulation and neurophysiological recordings in multiple brain areas and reveal the importance of inhibition and neuromodulation in the control of oscillation and synchrony. The outcome of the proposed work will provide us with innovative tools for brain investigation, novel insights regarding brain function, as well as providing tools for the diagnosis, monitoring and understanding of brain dysfunction.