(a) Extra [DA] at Light-On causes shorter latencies for non-engaged trials, but longer latencies for a subset of engaged trials. Top plot shows all trials (for the n=4 TH-Cre+ rats with ChR2 stimulation at Light-On for which video was recorded; 3 sessions/rat; 3336 no-laser trials in grey; 1335 laser trials in blue). Bottom plots show the breakdown into engaged (n=1975) and non-engaged (n=2696) trials. (b) We examined whether laser-slowed trials might be those in which the rat was waiting at the wrong port (if, for example, DA were to increase the salience of currently attended stimuli). Engaged trials were further broken down into “lucky guesses” (those trials for which the rat was immediately adjacent to the start port as it was illuminated) and “unlucky guesses” (immediately adjacent to one of the other two possible start ports). Blue dashed ellipses indicate zones used to classify trials by guessed port (8.5cm long diameter, 3.4cm short diameter) (c) Laser-slowing was observed for both lucky (n=603) and unlucky (n=1007) guesses. Note that blue distribution is bimodal in both cases, indicating that only a subset of trials were affected. Video observations suggested that on some trials extra [DA] evokes a small extra head/neck movement, that makes the trajectory to the illuminated port longer and therefore slower. (d) Quantification of trajectories, by scoring rat location on each video frame from 1s before Light-On to 1s after Center-In. Colored lines show all individual trajectories for one example session. Panels at right show the same trajectories plotted as distance remaining from Center-In port, by time elapsed from either Light-On or Center-In. Note that for non-engaged trials (green), the approach to the Center-In port consistently takes ~1-2s. Therefore, the epoch considered as “baseline” in the FSCV analyses (−3 to −1s relative to Center-In) is around the time that rats decide to initiate approach behaviors. (e) Extra [DA] causes longer average trajectories for engaged trials. Cumulative distributions of path-lengths between Light-On and Center-In, for (top-to-bottom) engaged/lucky, engaged/unlucky and non-engaged respectively. Blue lines indicate laser trials, and p-values are from Komolgorov-Smirnov tests comparing laser to no-laser distributions (no-laser/laser trial numbers: top, 292/75; middle, 424/99; bottom, 1897/792). On engaged trials rats often reoriented between the three potential start ports, perhaps checking if they were illuminated; one possibility is that the extra laser-evoked movement on engaged trials reflects dopaminergic facilitation of these orienting movements. If such a movement is already close to execution before Light-On, it may be evoked before the correct start port can be appropriately targeted. (f) Additional trajectory analysis, plotting time courses of rat distance from the illuminated start port. On non-engaged trials extra [DA] tends to make the approach to the illuminated start port occur earlier (note progressive separation of green, blue lines when aligned on Light-On). However, the approach time course is extremely similar (note overlapping lines in the final ~1-2s before Center-In), indicating that extra [DA] did not affect the speed of approach.