Parallel Excitatory and Inhibitory Neural Circuit Pathways Underlie Reward-Based Phasic Neural Responses

Figure 5

Acquired response of DA neurons. (a) The 99th trial: from the 1st to 99th trials, the model circuit receives a rewarding CS and a rewarding US. The result shows that, after learning, DA neurons exhibit a phasic peak upon rewarding CS and a baseline in response to reward outcome. (b) The 100th trial: the model circuit receives rewarding CS and nonrewarding US. The result shows that DA neurons exhibit a phasic peak when rewarding CS appears and exhibit a phasic dip at the time when the reward is expected. (c) The 199th trial: from the 101st to 199th trials, the model circuit receives nonrewarding CS and a nonrewarding US. The result shows that, after learning, the DA neurons exhibit a phasic dip upon nonrewarding CS and a baseline when there is no reward released at this trial. (d) The 200th trial: the model circuit receives nonrewarding CS and rewarding US. The result shows that DA neurons exhibit a phasic dip when nonreward CS appears and exhibit a phasic peak upon reward US. (e) The phasic activity of DA neurons under different situations. The thick red line indicates the activity of DA neurons at the 99th trial, the narrow blue line indicates the activity of DA at the 100th trial, the thick blue line indicates the activity of DA neurons at the 199th trial, and the narrow red line indicates the activity of DA neurons at the 200th trial. The yellow dashed line indicates the time at which CS appears and the green dashed line indicates the time at which rewards are released or not. (f) The physiological experimental result reprinted from Matsumoto and Hikosaka [5]. Red lines indicate reward trials, and blue lines indicate no reward trials. Full lines indicate reward CS-to-reward US (red) and nonreward CS-to-nonreward US (blue), while dashed lines indicate reward CS-to-nonreward US (blue) and nonreward CS-to-reward US (red).

(a)

(b)

(c)

(d)

(e)

(f)