This study investigates a biomarker of emotional state that has been previously identified in humans and validated in mice. The biomarker, based on beta-frequency communication between the amygdala (AMY) and hippocampus (HPC), is found to predict anxiety-related behavior in mice, both on long timescales (~30 minutes) and immediately preceding behavioral choices. The synchronization of somatostatin (SST+) interneurons in the basolateral amygdala (BLA) and ventral hippocampus (vHC) is a key driver of this biomarker. Specifically, the number and phase of beta-coherence bursts, which are transient periods of high beta-coherence, are strongly correlated with anxiety levels. Manipulating the phase and frequency of this synchronization bidirectionally alters anxiety-related behaviors. Optogenetic stimulation of SST+ interneurons in the BLA and vHC can increase or decrease anxiety behaviors, demonstrating that this synchronization is a causal driver of emotional state. The study also reveals that BLA-SST+ neurons directly inhibit vHC SST+ interneurons, suggesting a critical role in network synchronization. These findings provide new insights into the neural mechanisms underlying emotional processing and offer potential targets for treating anxiety disorders.This study investigates a biomarker of emotional state that has been previously identified in humans and validated in mice. The biomarker, based on beta-frequency communication between the amygdala (AMY) and hippocampus (HPC), is found to predict anxiety-related behavior in mice, both on long timescales (~30 minutes) and immediately preceding behavioral choices. The synchronization of somatostatin (SST+) interneurons in the basolateral amygdala (BLA) and ventral hippocampus (vHC) is a key driver of this biomarker. Specifically, the number and phase of beta-coherence bursts, which are transient periods of high beta-coherence, are strongly correlated with anxiety levels. Manipulating the phase and frequency of this synchronization bidirectionally alters anxiety-related behaviors. Optogenetic stimulation of SST+ interneurons in the BLA and vHC can increase or decrease anxiety behaviors, demonstrating that this synchronization is a causal driver of emotional state. The study also reveals that BLA-SST+ neurons directly inhibit vHC SST+ interneurons, suggesting a critical role in network synchronization. These findings provide new insights into the neural mechanisms underlying emotional processing and offer potential targets for treating anxiety disorders.