Figure 4.

The Gradual Maturation of Theta Sequences between P17 and P32 Is Correlated with the Emergence of Replay

(A) Examples of theta sequence emergence across development. Each plot shows a probability posterior derived from a single RUN session, where the x axis shows the proportion of time elapsed during the theta cycle and the y axis shows position on the track relative to the current location of the rat. The horizontal white line shows current rat location, and the vertical white lines demarcate one theta cycle. Hot colors show high decode probabilities. Numbers above the plots show theta sequence score, defined as the circular-linear weighted correlation of the probability posterior. Theta sequences are indicated by a shift in the decoded position from behind to ahead of the rat within the theta cycle: this emerges gradually between P17 and P32.

(B) Mean (±SEM) theta sequence scores in each age group. ^∗∗ indicates differences significant at p < 0.001 (1-way ANOVA comparison of age groups).

(C and D) Theta sequence scores are correlated with the distance covered (C) and speed (D) of replay trajectories during development. Each data point represents mean (±SEM) of all significant linear events in one experimental session for all developing rats. For each measure, r² and p values of linear regression over age are indicated above plots. Correlations reported in (C) and (D) remain significant even after controlling for age; see main text.

See also Figure S4.