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

Figure 4

The shift of DA and LHb neurons’ responses from US to CS. At the beginning of our simulation, the model circuit receives a reward CS and a reward US. FR: neural firing-rate activity. (a) Response of dopamine neurons in the 1st trial: DA neurons exhibit a phasic peak upon US before learning and do not respond to CS. (b) Response of DA neurons in the 2nd trial: the activity of DA neurons shows a peak upon CS and a peak upon US. The response upon US is weaker than the response in the 1st trial. The responses of DA neurons in the 3rd to 98th trials are similar to (b), but the peak upon US gets weaker over trials. (c) Response of DA neurons in the 99th trial: the activity of DA neurons shows a peak upon CS, but baseline responding to US after learning. (d) Response of LHb neurons in the 1st trial: LHb neurons exhibit a phasic dip upon US before learning and do not respond to CS. (e) Response of LHb neurons in the 2nd trial: the activity of LHb neurons shows a dip upon CS and a dip upon US. The response upon US is weaker than the response in the 1st trial. The responses of DA neurons in the 3rd to 98th trials are similar to (e), but the dip upon US gets weaker trial by trial. (f) Response of LHb neurons in the 99th trial: the activity of LHb neurons shows a dip upon CS, but baseline responding to US after learning. (a), (b), and (c) show the shift of DA neural response from US to CS after learning, while (d), (e), and (f) show the shift of LHb neural response. 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.

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