Gamma oscillations are widespread in the brain, and are thought to be important in organizing local activity within networks, as well as in “binding” information between them (Buzsáki, 2006; Fries et al., 2007; Singer, 1999; Varela et al., 2001). In this regard, is notable that two areas with prominent gamma oscillations, the hippocampus and frontal cortex (Bragin et al., 1995; Magill et al., 2005) both send functionally relevant projections to ventral striatum (Block et al., 2007; Goto and Grace, 2008; Ito et al., 2008), raising the possibility that gamma oscillations mediate the synchronization or “gating” of information flow between these areas. Gruber et al. (2009) examined the cross-coherence between ventral striatum, hippocampus, and frontal cortex during lever-pressing for reward, but their report did not include the gamma band. Recording from dorsal striatum, Tort et al. (2008) found gamma oscillations occurring at particular phases of the hippocampal theta rhythm, with the strength of this cross-frequency coupling dependent on task variables. These striatal gamma oscillations did not appear to be coherent with hippocampal gamma (see also DeCoteau et al., 2007), but our results suggest it would be of interest to determine the nature of this relationship for ventral striatal recording sites.
