Gene therapy has been used successfully to treat some intractable diseases. It has also been used in neurodegenerative diseases. The neuropeptides hypocretins (HCRT), also known as orexins, were discovered by two independent groups using different approaches. In 2000, examination of post-mortem tissue has revealed loss of the HCRT neurons in the brains of subjects with narcolepsy. Now it is abundantly clear that narcolepsy is neurodegenerative disease, as other markers that colocalize with HCRT are also absent in human with narcolepsy. In the case of narcolepsy there are two valid animal models of human narcolepsy, which permit hypothesis-driven testing of the efficacy of the gene transfer methodology. One can foresee that light stimulation of specific circuits will be used to manipulate behavior such as sleep, tremors in Parkinson's disease, or memory of fearful events in post-traumatic stress disorder.