Gamma Oscillations In The Rat Ventral Striatum Originate In The Piriform Cortex

Abstract

Local field potentials (LFP) recorded from the human and rodent ventral striatum (vStr) exhibit prominent, behaviorally relevant gamma-band oscillations. These oscillations are related to local spiking activity and transiently synchronize with anatomically related areas, suggesting a possible role in organizing vStr activity. However, the origin of vStr gamma is unknown. We recorded vStr gamma oscillations across a 1.4mm2 grid spanned by 64 recording electrodes as rats rested and foraged for rewards, revealing a highly consistent power gradient originating in the adjacent piriform cortex. Phase differences across the vStr were consistently small (<10{degrees}) and current source density analysis further confirmed the absence of local sink-source pairs in the vStr. Reversible occlusions of the ipsilateral (but not contralateral) nostril, known to abolish gamma oscillations in the piriform cortex, strongly reduced vStr gamma power and the occurrence of transient gamma-band events. These results imply that local circuitry is not a major contributor to gamma oscillations in the vStr LFP, and that piriform cortex is an important driver of gamma-band oscillations in the vStr and associated limbic areas.\n\nSignificance StatementThe ventral striatum is an area of anatomical convergence in circuits underlying motivated behavior, but it remains unclear how its inputs from different sources interact. One of the major proposals of how neural circuits may dynamically switch between convergent inputs is through temporal organization reflected in local field potential (LFP) oscillations. Our results show that in the rat, the mechanisms controlling vStr gamma oscillations are primarily located in the in the adjacent piriform cortex, rather than vStr itself. This provides a novel interpretation of previous rodent work on gamma oscillations in the vStr and related circuits, and an important consideration for future work seeking to use oscillations in these areas as biomarkers in rodent models of human behavioral and neurological disorders.