Major depressive disorder (MDD) significantly impacts the global population. MDD individuals often exhibit a negative processing bias, scrutinized through the approach-avoidance (Ap-Av) decision-making task. The fronto-cingulo-striatal (FCS) network, including the dorsolateral prefrontal cortex (dlPFC), subgenual anterior cingulate cortex (sgACC), pregenual anterior cingulate cortex (pACC) and striatum, is involved in MDD. Further, neural manipulations of the dlPFC and sgACC show promise in alleviating MDD symptoms. In non-human primates, beta-band oscillatory activity in the striatum correlates with decision-related variables, paralleling stimulation-induced negative bias. This suggests that FCS network interactions and neuronal synchronization may contribute to negative bias.To test this hypothesis, we recorded local field potentials in the FCS network simultaneously with microstimulation of the sgACC in two monkeys performing Ap-Av tasks. Two of 38 such stimulation increased avoidance choices, indicating sgACC involvement in negative bias.To analyze the relationship between beta oscillations and decision-making, we calculated beta response matrices (n = 3942) for the decision period. The responses were categorized into positive (n = 911) and negative (n = 591) groups. Microstimulation notably reduced the positive group, aligning with increased negative bias. Granger causality analysis on alpha (5-13 Hz) and beta (13-30 Hz) responses demonstrated diminished directional influences, particularly from dlPFC to pACC and striatum during negative bias.These findings suggest that beta synchrony mediates the top-down signal from dlPFC to the limbic system in processing negative bias. Reduction of this top-down influence may underlie the observed negative bias in decision-making, a hallmark symptom of MDD.