Two ERSP age-related oscillatory trends emerged from our feedback data, independent of feedback type. Early in feedback processing (50-150 ms), our 13-14-year-old adolescent group showed greater theta power than 15-17-year-olds and a trend in the same direction compared to 10-12-year-olds (see Figure 4C). Although we focused on a cluster of channels over the medial frontal cortex, the effects in these early temporal windows (i.e., ~0 to 200 ms post-stimulus) likely reflect the activation of different generators in the medial frontal cortex than those commonly attributed to the FRN. There is appreciable involvement of other sensory and association cortices during the early stages of stimulus processing, and future studies should consider, for example, differences in early occipital activation as a function of reward type, developmental stage, or their interactions. On the other hand, our 13-14-year-old adolescent group had larger burst of theta than the 10-12-year-oldsfor later processing of reward feedback (4-6 Hz, 300-400 ms), but not the 15-17-year-olds. This increase in mean evoked theta power likely reflects the engagement of generators in the medial frontal cortex and anterior cingulate that account for the FRN (Asada, Fukuda, Tsunoda, Yamaguchi, & Tonoike, 1999).
