Through selective activation/inhibition or dissection of neuronal circuits, optogenetic tools have raised hopes for a better understanding of neuropsychiatric mechanisms and therapeutic targets for various disorders. Although, overcoming serious limitations result in from conventional neuronal circuit study, this method has its own imperfections, such as optogenetic modulation of neural activity, using an internal, animal-generated, light source. In this review, limitations of external light delivery systems and possible approaches for using internal light sources in laboratory animals and perhaps, human being, are being addressed.