What, then, explains the complex pattern of gamma-50 power modulation? Clearly it is not simply a response to reward delivery; we observed an initial sharp peak, followed by a slower, sustained increase in power following reward receipt, but also increased power before movement initiation (turnarounds) in the absence of reward, and little modulation was observed during reward receipt on early laps. This latter observation suggests a learning component; further experimental manipulations are needed to test whether gamma-50 power following reward reflects learned value, some kind of error-related signal (“reward received as expected”), or other aspects of reward. It is theoretically possible that the gamma-50 signal we observed consists of multiple independent components, which are generated in anatomically distinct circuits but sum through volume conduction, such that the components appear indistinguishable on individual electrodes. In the absence of simple ways to test and verify such a scenario, an alternative possibility is that gamma-50 reflects different settings in which reward-related processing is engaged. There is a growing literature documenting representations of reward not being activated only by reward receipt itself, but also
