The spatial distribution of gamma-50 and gamma-80 on the track suggests a relationship to the reward sites. To further investigate the effect of rewards, we examined gamma power on error laps, where animals received no reward. Because errors were more frequent early in sessions (Figure 7C), when gamma-50 and gamma-80 power are not yet stable (Figures 5C,D) we compared error laps to a set of matched correct (rewarded) laps, by randomly choosing the preceding or following correct lap for each error lap (errors on lap 1, for which no preceding lap is available, were excluded to reduce bias). The spatial distributions for the error laps and matched correct laps are shown in Figures 7A,B. Gamma-50 power was increased at the reward sites on rewarded laps compared to error laps, while in contrast, gamma-80 power approaching and at the rewarded sites was similar on this spatial scale (but see Figure 9 for a finer-time scale analysis). We noted an increase in gamma-80 power on error laps on the segment following the second reward site; the significance of this is unclear (see Discussion).
