In this project, we will train mice to self-stimulate their direct pathway medium spiny neurons (dMSNs) using optogenetics. In prior work, we have found that mice find this behavior highly reinforcing. However, prior work gave mice at most 90 minutes of total training time. We plan to expand this by a factor of 100, giving the mice much more experience with this highly reinforcing behavior. We will examine behavioral changes in these mice, including assaying their motivation to receive stimulation, willingness to work for stimulation, and willingness to endure negative consequences to receive stimulation.