Reward-associated Gamma Oscillations in Ventral Striatum 1 Are Regionally Differentiated and Modulate Local Firing

20 Oscillations of local field potentials in the gamma range are found in many brain regions and 21 are supposed to support the temporal organisation of cognitive, perceptual and motor 22 functions. Even though gamma oscillations have also been observed in ventral striatum, one 23 of the brain’s most important structures for motivated behaviour and reward processing, their 24 specific function during ongoing behaviour is unknown. Using a movable tetrode array, we 25 recorded local field potentials and activity of neural ensembles in the ventral striatum of rats 26 performing a reward collection task. Rats were running along a triangle track and in each 27 round collected one out of three different types of rewards. The gamma power of local field 28 potentials on subsets of tetrodes was modulated by reward site visits, discriminated between 29 reward types, between baitedness of reward locations and was different before vs. after arrival 30 at a reward site. Many single units in ventral striatum phase-locked their discharge pattern to 31 the gamma oscillations of the local field potentials. Phase-locking occurred more often in 32 reward-related than reward–unrelated neurons and LFPs . A substantial number of 33 simultaneously recorded local field potentials correlated poorly with each other in terms of 34 gamma rhythmicity, indicating that the expression of gamma activity was heterogeneous and 35 regionally differentiated. The orchestration of local field potentials and single unit activity by 36 way of gamma rhythmicity sheds light on the functional architecture of the ventral striatum 37 and the temporal coordination of ventral striatal activity for modulating downstream areas and 38 regulating synaptic plasticity. 39 40