When analyzing changes in activation across sessions, we compared
intra-session contrasts of positive N negative feedback to control for potential
effects of time or separate scanning sessions on the BOLD signal
for individual conditions. Therefore, to examine differences in feedback
sensitivity BEFORE and AFTER the manipulation, we compared feedback
sensitivity (positive N negative) BEFORE versus AFTER the manipulation
using the contrast AFTER (positive N negative feedback) N BEFORE
(positive N negative feedback). Valence sensitivity declined after the
manipulation in the ventral striatum, as well as parts of the occipital
cortex and cerebellum (Fig. 6A; Table 2), which is consistent with decreases
in task engagement that were reported by the subjects (see Discussion
section).
To better understand the source of this effect, we examined the parameter
estimates for positive and negative feedback separately within
the ventral striatum. The decline in valence sensitivity within the
ventral striatum was driven more strongly by an attenuated decrease
in activation following negative feedback, which was marginally higher
(less negative) AFTER the manipulation than BEFORE, t(24) = 1.75, p =
0.093. The decrease in positive feedback activation AFTER the manipulation
was not significant, t(24) = 0.63, p = 0.533; however, the more
subtle decreases in positive feedback combined with nearly significant
increases in negative feedback activation contributed to a significantly
reduced valence sensitivity.