Figure 1. Rats Learn to Perform Specific Three-Step Lever-Press Sequences.

(A) Task procedure with examples of a correct sequence (1–2-1, top) and an incorrect sequence (1-2-2, bottom), and top view of operant chamber configuration (right).

(B) Percent correct in total session (solid) and in the best 3-min performance period (dashed) across training days (n = 13 rats). Only 4 unimplanted rats were trained past day 40. Shading indicates SEM.

(C) Number of correct trials performed during best 3-min performance period across training days (n = 13 rats).

(D) Head tracking data from 30 consecutive correct trials in one training session (top). Average session trajectory (dark blue to yellow) of rat performing the 1-2-1 sequence (bottom) with head locations for lever 1 presses (green), lever 2 presses (blue), and chocolate milk delivery (brown).

(E) Side-to-side (top) and forward-and-back (bottom) session average head trajectories from 7 consecutive training days for a rat performing the 1-2-1 sequence (left) and another rat performing the 1-2-2 sequence (right).

(F) Correlation coefficients of session average head trajectories between pairs of rats that learned different sequences (left, n = 42 pairs), session average trajectories within single rats (middle, n = 7 rats), and trial average trajectories within rats (right, n = 7 rats). Only trajectories from days 10+ of training with successful video tracking were used. Error bars indicate SEM. **p < 0.001 (Wilcoxon rank-sum test).

(G) Ratio of trials performed in 30-min devaluation probe session and number of trials performed in the first 30 min of prior day’s training session as a function of number of days trained. Each data point corresponds to a single session.