Similarly, using a dual infection strategy (Stauffer et al., 2016), injected the VTA of rhesus monkeys with a mixture of the Cre-dependent ChR2 optogenetic activator (pAAV5-DIO-Ef1α-ChR2(h134)-EYFP) and a virus expressing Cre attached to a tyrosine-hydroxylase (TH) promoter (AAV2/9-rTH-PI-Cre-SV40). This evidence concerns the gene TH and infection.