Aspects of the disclosure include devices, systems and methods for optogenetic modulation of action potentials in target cells. The subject devices include light-generating devices, control devices, and delivery devices for delivering vectors to target cells. The subject systems include light-activated proteins, response proteins, nucleic acids comprising nucleotide sequences encoding these proteins, as well as expression systems that facilitate expression of these proteins in target cells. Also provided are methods of using the subject devices and systems to optogenetically inhibit and intercept action potentials in target cells, e.g., to treat a neurological or psychiatric condition in a human or non-human animal subject.