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

Figure 6

Acquired response of LHb neurons. (a) The 99th trial: from the 1st trial to the 99th trial, the model circuit receives rewarding CS and rewarding US. The result shows that, after learning, LHb neurons exhibit a phasic dip upon rewarding CS and a baseline activity in response to rewarding outcome. (b) The 100th trial: the model circuit receives rewarding CS and nonrewarding US. The result shows that LHb neurons exhibit a phasic dip when rewarding CS appears and exhibit a phasic peak at the time when the reward should be released. (c) The 199th trial: from the 101st trial to the 199th trial, the model circuit receives nonrewarding CS and nonrewarding US. The result shows that, after learning, LHb neurons exhibit a phasic peak upon nonrewarding CS and a baseline activity due to omission of reward at this trial. (d) The 200th trial: the model circuit receives nonrewarding CS and rewarding US. The result shows that LHb neurons exhibit a phasic peak when nonrewarding CS appears and exhibit a phasic dip upon rewarding US. (e) The phasic activity of LHb neurons under different situations. The thick red line indicates the activity of LHb at the 99th trial, the narrow blue line indicates the activity of LHb at the 100th trial, the thick blue line indicates the activity of LHb at the 199th trial, and the narrow red line indicates the activities of LHb 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 results reprinted from Hong and Hikosaka [2]. Red lines indicate reward trials, and blue lines indicate no reward trials. Thick lines indicate reward CS-to-reward US (red) and nonreward CS-to-nonreward US (blue), while narrow lines indicate reward CS-to-nonreward US (blue) and nonreward CS-to-reward US (red).

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