Figure 2.

Changes in firing in response to positive and negative reward prediction errors (PE's) in rat dopamine (DA) and basolateral amygdala (ABL) neurons. Rats were trained on a simple choice task in which odors predicted different rewards. During recording, the rats learned to adjust their behavior to reflect changes in the timing or size of reward. As illustrated in the left panel, this resulted in delivery of unexpected rewards (+PE) and omission of expected rewards (−PE). Activity in reward-responsive DA and ABL neurons is illustrated in the heat plots to the right, which show average firing synchronized to reward in the first and last 10 trials of each block, and in the scatter/histograms below, which plot changes in firing for each neuron in response to +PE's and −PE's. As described in the text, neurons in both regions fired more to an unexpected reward (+PE, black arrow). However only the DA neurons also suppressed firing on reward omission; ABL neurons instead increased firing (−PE, gray arrows). This is inconsistent with the bidirectional error signal postulated by Rescorla-Wagner or TDRL and instead is more like the unsigned error signal utilized in attentional theories, such as Pearce-Hall. Figure adapted from Roesch, Calu, and Schoenbaum (Roesch et al., 2007) and Roesch, Calu, Esber, and Schoenbaum (Roesch et al., 2010).