Low- and high-gamma oscillations deviate in opposite directions from zero-phase synchrony in the limbic corticostriatal loop

The loop structure of cortico-striatal anatomy in principle enables both descending (cortico-striatal) and ascending (striato-cortical) influences, but the factors that regulate the flow of information in these loops are not known. We report that low- and high-gamma oscillations (∼50 and ∼80 Hz, respectively) in the local field potential of freely moving rats are highly synchronous between the infralimbic region of the medial prefrontal cortex (mPFC) and the ventral striatum (vStr). Strikingly, high-gamma oscillations in mPFC preceded those in vStr, whereas low-gamma oscillations in mPFC lagged those in vStr, with short (∼1 ms) time lags. These systematic deviations from zero-phase synchrony were consistent across measures based on amplitude cross-correlation and phase slopes and were robustly maintained between behavioral states and different individual subjects. Furthermore, low- and high-gamma oscillations were associated with distinct ensemble spiking patterns in vStr, even when controlling for overt behavioral differences and slow changes in neural activity. These results imply that neural activity in vStr and mPFC is tightly coupled at the gamma timescale and raise the intriguing possibility that frequency-specific deviations from this coupling may signal transient leader-follower switches.