In one example, a system electrically stimulates target cells of a living animal using an elongated structure, a modulation circuit and a light pathway such as provided by an optical fiber arrangement. The elongated structure is for insertion into a narrow passageway in the animal such that an end of the elongated structure is sufficiently near the target cells to deliver stimulation thereto. The modulation circuit is for modulating the target cells while the elongated structure is in the narrow passageway, where the modulation circuit is adapted to deliver viral vectors through the elongated structure for expressing light responsive proteins in the target cells. The light pathway is used for stimulating the target cells by delivering light to the light-responsive proteins in the target cells.