Figure 4. DRN^5-HT ensembles are excited during exploration under potential threat.

A) Diagram of an elevated plus maze showing a mouse engaged in peeking behavior.

B) Fraction of the total session time spent in open arms/center versus closed arms. The red dotted line indicates no preference for either zone, and error bars represent ±SEM. N = 13 mice. One-sample t-test comparing open arm and center time to a theoretical mean of 50%, p < 0.0001.

C) Comparison of population-level activity between open arms/center and closed arms. Error bars represent ±SEM. p = 0.0054, two-tailed paired t-test, n = 13 mice.

D) Comparison of activity in open arms/center and closed arms for individual cells. Cells with a significant preference are color-coded (shuffle test, α < 0.05). The dotted line represents no difference in activity between zones. n = 304 cells in 12 mice.

E) Calcium activity from an example cell indicating relevant behavioral events: head dips (orange) and peeking (purple). Epochs during which the mouse occupied the open arms or center are shaded pink.

F) Relative proportion of open arm-excited cells across all animals (47%, n = 304 cells in 12 mice, shuffle test, α < 0.05), and the fraction of open arm-excited cells (n = 143) that are also excited by head dip (64%) and peeking (69%), and inhibited by closed arm re-entry (56%).

G) Relationship between an animal’s proportion of open arm-excited cells and time spent in the open arms and center. The purple line is a best-fit by linear regression (p = 0.0058, R² = 0.387, n = 18 mice). Shading represents 95% confidence interval.

H) The two largest ensembles from a representative animal. Ensemble 1 is significantly excited in the open arms and center (p = 0.007), while ensemble 2 is non-selective for arm type (p =0.922). Occupancy of the open arms and center is indicated in pink, head dips in purple, and peeking in blue.

I) Spatial distribution of ensembles in (H).