Expectations, gains, and losses in the anterior cingulate cortex

The anterior cingulate cortex (ACC) participates in evaluating actions and outcomes. Little is known on how action/reward values are processed in ACC and if the context in which actions are performed influences this processing. Here we report ACC unit activity of monkeys performing two tasks. The first tested whether the encoding of reward values is context-dependant i.e. dependant on the size of the other rewards available in the current block of trials. The second task tested whether unexpected events signaling a change in reward are represented. We show that the context created by a block design (i.e. the context of possible alternative rewards) influences the encoding of reward values, even if no decision or choice is required. ACC activity encodes the relative and not absolute expected reward values. Moreover, cingulate activity signals and evaluates when reward expectations are violated by unexpected stimuli indicating reward gains or losses