A different view of the differential modulation of gamma-50 and gamma-80 oscillations can be obtained from their temporal relationship to reward-related events. Figure 9A shows the average gamma-50 (left column) and gamma-80 (right) power around the time of the rat's arrival at the feeder sites (time 0). Because pellet release was triggered when rats crossed the reward trigger lines some distance in front of the reward sites (see Figure 2A), and pellets took up to 2 s to arrive at the track, the rats tended to arrive before the pellets, catching the pellets in their mouth. Comparing gamma-50 and gamma-80 power over all correct laps (Figure 9A, grey line), gamma-50 power showed a clear peak following reward receipt, while gamma-80 was strongly decreased. At both frequencies, this initial transient was followed by a more sustained increase (or alternatively, a fast transient was superimposed on a slow, sustained increase). For both gamma-50 and gamma-80, these transient responses were absent during non-rewarded error laps (red line) but not from matched rewarded laps (blue line), indicating that the presence or absence of reward
