Many of the studies discussed above involved simultaneous recordings from mPFC and dorsal CA1; however, only ventral CA1 projects directly to mPFC [8,9]. The ventral hippocampus has functions that differ from the dorsal hippocampus, including regulation of anxiety-related behaviors [28]. A recent study recorded in mPFC and ventral and dorsal CA1 in order to investigate whether interregional oscillatory phase-locking influences the effects of anxiety on behavior [18••]. In anxiety-inducing environments, including an elevated plus maze, positive correlations were observed between mPFC and ventral, but not dorsal, hippocampal theta rhythms, and mPFC cells were strongly phase-locked to ventral hippocampal theta. Remarkably, theta power in mPFC and coherence between mPFC and ventral hippocampus decreased immediately before animals entered anxiety-inducing zones of the maze and increased when animals entered the ‘safe’ closed arms of the maze, even though there were no significant differences in running speed between these two behaviors. These findings suggest the intriguing hypothesis that theta phase-locking between the ventral hippocampus and mPFC inhibits anxiety-provoking behaviors.
