Figure 1. Experimental framework.

(A) Timeline for a single experiment. AIMs Test – Abnormal Involuntary Movement testing (see ‘Dopamine neuron stimulation induces context- and history-dependent abnormal involuntary movements’). The ‘ChR2 between’ group also received ‘during reach’ stimulation after ‘occlusion’ sessions (see Figure 11). (B) Light was physically occluded from entering the brain by obstructing the connection between the optical fiber and patch cable during ‘occlusion’ sessions. (C) Rats were assigned to one of five groups based on virus injected and timing of optogenetic manipulation. n is the number of rats included in the analysis for each group (see Materials and methods). Dot colors correspond with the color used to represent each group in subsequent figures. (D) A single skilled reaching trial. 1 – rat breaks IR beam at the back of the chamber to request a sugar pellet (‘beam break’). 2 – Real-time analysis detects the paw breaching the reaching slot to trigger 300 fps video from 1 s before to 3.33 s after the trigger event (‘video trigger’). 3 – 2 s after the trigger event, the pellet delivery rod resets and the rat can initiate a new trial (‘intertrial interval’). Optogenetic manipulations occurred either during reaching (beam break to 3 s after ‘video trigger’) or between reaches (beginning 4 s after ‘video trigger’ and lasting 5 s). Figure 1—figure supplement 1 shows the distribution of the duration of ‘during reach’ laser-on epochs. (E) Double-floxed ChR2-EYFP, Arch-EYFP, or control EYFP constructs were injected bilaterally into SNc. (F) Immunohistochemistry against EYFP showing expression of a fused ChR2-EYFP construct in the nigrostriatal pathway. Optical fibers (arrow) were implanted over SNc contralateral to the rat’s preferred reaching paw. Estimated locations of all fiber tips are shown in Figure 1—figure supplement 2. Representative immunohistochemistry images from each group are shown in Figure 1—figure supplement 3. Scale bar = 1 mm.

Figure 1—figure supplement 1. The duration of ‘during reach’ and ‘between reach’ stimulation is closely matched.

(A) Distribution of the duration of ‘during reach’ stimulation for all ‘ChR2 during’ rats. The median duration of ‘during reach’ stimulation was 5.37 s compared to 5 s for ‘between reach’ stimulation (sign test: Z = 18.96, p=1.89×10⁻⁸⁰). (B) Same as (A) for each rat individually. (C) Distribution of the duration of ‘during reach’ inhibition for all ‘Arch during’ rats. The median duration of ‘during reach’ inhibition was 5.75 s compared to 5 s for ‘between’ reach inhibition (sign test: Z = 25.46, p=2.53×10⁻¹⁴³). (D) Same as (C) for each rat individually. Dashed lines represent median ‘during reach’ durations. Solid lines at 5 s represent duration of ‘between reach’ stimulation for comparison.

Figure 1—figure supplement 2. Optical fiber locations.

(A) Circles indicate optical fiber tip locations in rats analyzed from each group superimposed on coronal rat brain atlas images (Paxinos and Watson, 1998). X’s indicate optical fiber tip locations of rats excluded from the analysis due to either fiber misplacement or lack of opsin expression (see Materials and methods). (B) Optical fiber tip locations superimposed on sagittal rat brain atlas images. (C) Three-dimensinal optical fiber tip locations for each group. Small dots represent individual rats. Large dots represent average locations for each group. A-P and M-L coordinates are with respect to bregma; D-V coordinates are with respect to the brain surface. (D) Three-dimensional A-P, M-L, and D-V coordinates for each fiber tip. There were no significant differences in fiber tip locations between groups along any axes (one-way ANOVAs: A-P: F(4, 25)=0.28, p=0.89; M-L: F(4, 25)=0.38, p=0.82; D-V: F(4, 25)=0.95, p=0.45). Gray dots represent locations for individual rats.

Figure 1—figure supplement 3. Representative immunohistochemistry against EYFP showing expression of fused opsin-EYFP constructs in the nigrostriatal pathway for all groups.

Images on the left (‘Analyzed Rats’) show examples of immunohistochemistry from rats that were included in analyses for each group. Images on the right (‘Excluded Rats’) show examples of immunohistochemistry from rats that were excluded from analyses for each group. Reasons for exclusion from top to bottom: ChR2 During – optical fiber tip ventral to SNc and weak opsin expression; ChR2 Between – optical fiber tip ventral to SNc; Arch During – optical fiber tip rostral to SNc; EYFP – optical fiber tip rostral to SNc. Scale bar = 1 mm.