Moreover, Selleck PI3K inhibitor studies in animals demonstrated that the BLA is particularly critical for normal performance in a variety of settings that require knowledge of current outcome values including reversal learning and second-order conditioning (Lindgren et al., 2003; Schoenbaum et al., 2003; Johnson et al., 2009). Thus, our finding of a predictiveness signal in the BLA supports the view that the predictive value of CSs is critical for amygdala responses during fear conditioning. On the one hand, the BLA has been highlighted as a site of plasticity in associative learning that is relevant for learning and maintaining CS–US associations (Maren
& Quirk, 2004; Reijmers et al., 2007; Ehrlich et al., 2009; Pape & Pare, 2010), and CS and US information is assumed to converge in this region (Barot et al., 2008). Thus, increasing predictiveness and concomitant increased BOLD responses in the BLA might reflect strengthening of the associative memory with regard to CS–US contingencies. This assumption would, however, require that associative learning also selleck inhibitor occurs in the CS– condition as the predictiveness signal shows equal characteristics for CS100 and CS–. On the other hand,
some recent studies demonstrated that learning of CS–US associations increased over time, when subjects were contingency aware (Schiller et al., 2010; Raio et al., 2012). These findings reflect the observed time course of the predictiveness signal in the current study. Predictiveness might therefore also reflect contingency awareness, which is likely to increase with increasing reliability of outcome predictions. To strengthen the finding of separate recruitment of the BLA and CM by predictiveness and surprise signals, we directly compared the mean activity in both regions. Unsigned PEs were found to correlate with signal changes in the CM but not BLA, whereas the opposite was true for predictiveness signals indicating a clear functional dissociation of both regions. With respect to interactions between the BLA and CM during the process of aversive learning in humans, we can only speculate
as the current study does not allow the drawing of firm conclusions. However, as projections from the TCL BLA to the CM are not reciprocated in the amygdala (Pape & Pare, 2010), we would assume that the surprise signals in the CM project onto cortical areas, which then project back to the BLA where predictiveness as a derivative of these signals controls learning of cue–outcome associations. To summarize, we extended recent findings of PH-like learning signals in the amygdala (Li et al., 2011) by investigating CS- and US-related processing in an RW/PH hybrid model of reinforcement learning. By combining this approach with high-resolution fMRI, we demonstrate a unique functional dissociation of amygdala subregions during associative learning in humans.