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Manipulating the revision of reward value during the intertrial interval increases sign tracking and dopamine release

Fig 1

Sign tracking is more prominent during sessions with 120-s ITIs.

(A) Response bias, which is (Lever Presses − Food Cup Entries) / (Lever Presses + Food Cup Entries). (B) The probability difference, which is (P_lever − P_receptacle). (C) Latency index, which is ( Cup Entry Latency − Lever Press Latency) / 8. (D) PCA index = average of response bias, probability difference, and latency difference indices described in A–C. All of these ratios range from −1.0 to +1.0 and are more positive and negative for animals that sign track and goal track, respectively. All behavioral indices are derived from sessions during which DA was recorded (60-s ITI groups = 7 rats; 120-s ITI group = 12 rats) and used behavior during the entire 8-s CS epoch. Each of the above distributions was computed by session. Supporting material reports results by rat. (E-F) PCA index computed using just the first 4 s (E) and last 4 s (F) of the CS period;120-s ITI group = red; 60-s ITI group = blue. (G) Average beam break (solid) and lever press (dashed) rate for 120-s (red) and 60-s (blue) ITI sessions. (H) Average lever press rate for 120-s (red) and 60-s (blue) ITI sessions. Data are the same as in G but with a smaller scale so that differences and timing can be better visualized. Error bars represent SEM. (I) Green lines are the difference between solid blue and solid red lines from “G” (food cup entries for the 120-s ITI group minus food cup entries for the 60-s ITI group) during the cue period. Thus, negative deflections illustrate more food cup entries during sessions with a 60-s ITI. Orange lines represent the differences between the 120-s ITI group lever pressing and the 60-s ITI group lever pressing (i.e., red dashed minus blue dashed from “H”). Thus, positive deflections represent time during the cue period when rats in the 120-s ITI group lever pressed more than those in the 60-s ITI group. Orange and green tick marks represent 100-ms bins in which there was a significant difference between 120-s and 60-s ITI groups (t test; p < 0.05). Percentages for each session were computed and then averaged across sessions. Underlying data for Fig 1 can be found in S1 Data. For analysis averaged within session and rat, and then averaged across rats, please see S2 Fig. CS, conditioned stimulus; DA, dopamine; GT, goal tracking; ITI, intertrial interval; P_lever, probability of pressing lever; P_receptacle, probability of entering the receptacle; PCA, Pavlovian Conditioned Approach; ST, sign tracking; US, unconditioned stimulus.

doi: https://doi.org/10.1371/journal.pbio.2004015.g001