The grand challenge in biomedical engineering is to develop methods for interfacing optical stimuli with the nervous system. LIGHT4BRAIN aims at developing near-infrared-sensitive semiconductive polymer and photochromic nanoparticles as non-genetic light actuators for neuronal activation in the central nervous system. Goal is to interrogate specific brain circuits and compensate for nervous system pathologies in which neuronal degeneration has induced a specific loss of function. Current implant technologies using microelectrodes for delivering electrical signals meet several problems that limit the performance and safety of the implants. LIGHT4BRAIN innovation consists in using biocompatible organic nanoparticles for lightdriven neuronal activation via seamless interfaces that can mimic the physiological activation of neural circuits. This is a step forward with respect to existing nanoparticle-based technologies that perform hyperthermia or drug release or to optogenetics that implies gene therapy. Demonstrations of LIGHT4BRAIN phototransducers will address physiopathological states involving the visual and prefrontal cortices. Nanoparticles can be functionalized with single chain antibodies to target specific neuronal populations or orthogonally bound to targeting carriers and administered in the liquid phase by stereotaxic injection in the region of interest. Photoactive nanoparticles are not endocytosed, preserve their location and activity in the biological environment for long times and stimulate the targeted neurons by a capacitive depolarizing effect that brings neurons to fire action potentials. LIGHT4BRAIN will represent a new method for interfacing optical stimuli with the nervous system in order to address nervous system pathologies in which neuronal degeneration, inflammation or abnormal circuit activity has induced a specific loss of function (e.g., vision, psychiatric diseases).