The BOLD response in the vmPFC/mOFC is positively correlated with the temporally discounted subjective reward expectation (Kable and Glimcher, 2007 and Prévost et al., 2010). Prevost et al. (2010)

argue that vmPFC/mOFC does not encode the effort to be expended in reaching the reward. Croxson et al. (2009) have also reported the existence of a more lateral posterior OFC region that is sensitive to expectations about reward magnitude but which does not carry information about the effort to be exerted before a reward is received. Exactly EX 527 in vivo how ACC encodes effort remains uncertain. Although both Croxson et al. (2009) and Prévost et al. (2010) report that ACC activity reflects both anticipated effort and anticipated reward there are differences between the patterns of modulation seen in the two studies. The differences may reflect the degree to which cueing of effort expectations and actual

RO4929097 order effort exertion are separated in time. When the cue that indicates the reward and effort expectations is separated in time from the period when the response is made and effort is actually exerted then different BOLD signals at the two times can be identified (Croxson et al., 2009). At the time that an instruction cue is presented the ACC signal reflects the interaction of both reward and effort expectations; the ACC is most active in anticipation of high rewards to be obtained with the least effort. As the participant begins to engage in the “effort period” and makes a series of movements, the ACC signal increases as the reward approaches (Figure 8). Comparisons have also been made of single neuron activity in the ACC and OFC when monkeys of are presented

with cues instructing reward and effort expectations (Kennerley et al., 2009) and as they move through a sequence of responses toward rewards (Shidara and Richmond, 2002 and Simmons and Richmond, 2008). In the experiment conducted by Kennerley et al. (2009) animals chose between two cues with learned associations with expected reward payoff size, probability of reward delivery, and effort (expected number of lever presses). In both ACC and lOFC, neurons were equally sensitive to each facet of value. Single ACC neurons, however, were significantly more likely to encode all three aspects of value. In other words, the activity of single neurons in the ACC integrates information about the effort costs and the reward benefits of actions and does not distinguish what aspect of a choice makes it valuable (Figure 9).