(A) Injection of AAV5-DIO-ChR2 into VTA of TH::Cre mice. (B) Confocal image: ChR2-eYFP expression in VTA, colocalization with TH (blue). Scale bar: 100 µm. (C) In vivo anesthetized recording of light-evoked spikes from TH::Cre mouse: ChR2 in VTA. (D) Optical stimulation parameters for home cage interaction. For excitation, 473nm light was delivered in 30 Hz bursts (8 pulses, 5 ms each) every 5 seconds. For inhibition, continuous 591nm light was delivered. (E) Summary of light-evoked changes in social interaction after bidirectional control of DA neurons. Phasic stimulation of VTA cell bodies increased social interaction compared to eYFP (n=17 ChR2 and n=18 eYFP, LME model, t57=2.31, p=0.03), while inhibition of VTA cell bodies decreased interaction (n=10 eNpHR3.0 and n=15 eYFP, LME model, t57=−2.09, p=0.04). (F) Neither stimulation nor inhibition of VTA cell bodies significantly affected novel object interaction (p>0.05). See also Figure S2.