While examples of entrainment of striatal FSIs to gamma oscillations have been documented before (Berke, 2005; Kalenscher et al., 2008), we found distinct FSIs cohering with gamma-50 and gamma-80, as well as FSIs changing their firing rate differentially with gamma-50 and gamma-80 power. This suggests that, regardless of the origin of the field potential, there are local effects of gamma-50 and gamma-80, mediated by at least partially distinct populations of ventral striatal neurons. Bracci et al. (2003) reported that the frequency of FSI intrinsic subthreshold membrane oscillations could be increased (from about 45 to about 80 Hz on average; their Figure 4B) by increasing the amount of injected current. This suggests that individual FSIs are, in principle, capable of expressing the range of oscillation frequencies considered here, and might switch between different oscillation frequencies given appropriate stimulation. However, we observed a partial separation between gamma-50 and gamma-80 in terms of FSI firing rate tuning and coherence; whether this distinction arises from differences in afferent input or neuromodulation, intrinsic properties, or their interaction, remains to be determined. As suggested by the
