Figure 6. Fiber photometry assessment of DA projection activity in NAc during social interaction.

(A) Fiber photometry of VTA projections in NAc. (B) VTA projection activity during social (top) and novel object investigation (bottom; interaction bouts in red). (C) Heatmaps (top) and peri-event plots (bottom) of NAc projection fluorescence aligned to start of interaction bout for social or novel object investigation. For heatmaps, warmer colors indicate higher fluorescence signal; peri-event plots: warmer colors indicate earlier interaction bouts. (D) NAc projections largely recapitulate social signals in VTA, with lower response to novel object (n=11, Wilcoxon signed-rank test, mean peak fluorescence: 6.9% dF/F social, 3.6% dF/F novel object, p=0.016). (E) Decay of NAc projection signal across bouts. Decay in signal during social behavior is slower in projections than cell bodies. Social decay rate=0.2491, r²=0.8; Object decay rate=0.0012, r²=0.6. (F) Directed graphical model of causal mediation analysis; while time elapsed partially mediated effects of VTA-NAc projection activity on latency to social interaction, the major effect was direct (68.2% average direct effect, 31.8% average indirect effect mediated by time elapsed; both p<0.0001). No significant direct or indirect effects of VTA-NAc projection activity on latency to interact were observed in novel object investigation.