Gamma-50 oscillations in rat ventral striatum have previously been related to movement initiation (Masimore et al., 2005) and to reward receipt (Berke and Kunec, 2004; Kalenscher et al., 2008). In such freely moving paradigms (including ours) reward receipt tends to be correlated with other aspects of behavior, such as movement cessation, pausing, and movement initiation, making the precise correlates of gamma-50 difficult to identify. Several aspects of the present analysis address this issue. First, the temporal profile of gamma-50 power (Figure 9) shows a clear peak following reward receipt. The observation that this peak was absent from matched control laps where no reward was received suggests that it results from reward receipt; however, in principle it is possible that differences in behavior on rewarded vs. non-rewarded trials, rather than the presence or absence of reward per se, could account for this gamma-50 pattern. Rewarded and non-rewarded trials have at least movement cessation (stop running) and movement initiation (start running) in common, thus those factors cannot account for the observed difference. A possibility is that gamma-50 is associated with appetitive approach
