In general, in the absence of clear phase reversals such as those observed relative to hippocampal cell layers (Buzsáki et al., 1983), or without current source density analysis, the possibility that field potentials are volume-conducted from elsewhere in the brain instead of generated locally is difficult to exclude. Specifically, it has been suggested that ventral striatal gamma oscillations may include contributions from nearby piriform cortex (Berke, 2005), where gamma power is prominent (Kay and Freeman, 1998). However, there is evidence that such an explanation cannot account for the full range of gamma oscillations observed in the striatum. Recording from putative FSIs in anesthetized rats, Sharott et al. (2009) found the phase relationship between gamma oscillations in cortex and a range of sites across the striatum to be inconsistent with volume conduction. Furthermore, oscillations in the gamma range have been found using intracellular recordings in identified PV+ FSIs in the striatum (Bracci et al., 2003; ventral striatum specifically: Taverna et al., 2007). In vitro studies of such striatal FSIs have revealed prominent subthreshold oscillations in the 50 Hz range. Importantly, these
