Figure 6. Phasic dopamine manipulations affect both learning and motivation.

(a) FSCV measurement of optogenetically-evoked [DA] increases. Optic fibers were placed above VTA, and [DA] change examined in nucleus accumbens core. Example shows dopamine release evoked by a 0.5s stimulation train (average of 6 stimulation events, shaded area indicates +/−SEM). (b) Effect of varying the number of laser pulses on evoked dopamine release, for the same 30Hz stimulation frequency. (c) Dopaminergic stimulation at Side-In reinforces the chosen left or right action. Left, in TH-Cre⁺ rats stimulation of ChR2 increased the probability that the same action would be repeated on the next trial. Circles indicate average data for each of 6 rats (3 sessions each, 384 trials/session ± 9.5 SEM). Middle, this effect did not occur in TH-Cre⁻ littermate controls (6 rats, 3 sessions each, 342±7 trials/session). Right, in TH-Cre⁺ rats expressing Halorhodopsin, orange laser stimulation at Side-In reduced the chance that the chosen action was repeated on the next trial (5 rats, 3 sessions each, 336±10 trials/session). See Supplementary Fig.8 for additional analyses. (d) Laser stimulation at Light-On causes a shift towards sooner engagement, if the rats were not already engaged. Latency distribution (on log scale, 10 bins per log unit) for non-engaged, completed trials in TH-Cre⁺ rats with ChR2 (n=4 rats with video analysis; see Supplementary Fig.9 for additional analyses). (e) Same latency data as d, but presented as hazard rates. Laser stimulation (blue ticks at top left) increases the chance that rats will decide to initiate an approach, resulting in more Center-In events 1-2s later (for these n=4 rats, one-way ANOVA on hazard rate F(1,3) = 18.1, p=0.024). See Supplementary Fig.10 for hazard rate time courses from the individual rats.