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 opposing gradients of high voltage spindle-entrained FSIs in dorsolateral striatum and high gamma power in ventromedial striatum (Berke et al., 2004), such differences are unlikely to be homogeneous throughout the striatum. A limitation of the current data set is that we sampled a relatively large area within ventral striatum that likely includes relevant anatomical and cytological distinctions (Pennartz et al., 1994; Zahm and Brog, 1992), raising the possibility of segregation between gamma-50 and gamma-80 generation and/or relevance, obscured by lack of anatomical specificity in our data. Nevertheless, the separation between gamma-50 and gamma-80 related FSIs provides an entry point that can be connected to membrane properties and their dependence on neuromodulators such as dopamine (Bracci et al., 2002; Costa et al., 2006; Dejean et al., 2008), as well as to differences in FSI firing correlates (Berke, 2008; Sharott et al., 2009) in further experiments.
