Extended Data Fig. 4: Behavioral timescale sequences across animals, remapping types, and environments.
From: A flexible hippocampal population code for experience relative to reward
a) Reward-relative sequences on the last switch (day 14) for all mice not shown in Fig. 4a. In (a, c–e), circular-circular correlation coefficient (rho) of sequence order, p-value from two-sided permutation test, and n of cells are shown for each mouse. b) Population-level remapping from all place cells in example mouse m14 upon the novel environment switch (day 8). In (b, c), left two panels: cross-validated sort by firing order in Env 1; right-hand panel: cross-validated sort by firing order in Env 2. c) Remapping (or lack thereof) of specific subpopulations in mouse m14 upon the novel environment switch (day 8). Top: reward-relative (RR) sequences are preserved across environments; Middle: a subset of track-relative place cells retain their firing order across environments, especially at the beginning of the track; Bottom: non-RR remapping cells remap globally, mirroring the overall population. d, e) Example sequences of disappearing cells (d) and appearing cells (e) from mouse m14 on the last switch (day 14). In (d, e), cross-validated sort was performed on the trials in which cells had significant spatial information (before for disappearing, after for appearing). Left: before switch; Right: after switch. f) Example mean ± SEM licking (top) and distribution of RR sequence peak firing positions (bottom) during trials before the switch, aligned to the start of the reward zone. Left: example narrow RR sequence (low circular variance around reward); Right: example broad sequence (high circular variance). Note more precise licking coinciding with a sequence that is more dense around the reward zone (left). Vertical gray dashed lines, reward zone start and surrounding ±50 cm. g) Same as (f), but showing example licking and RR sequences for trials after the switch. h) RR sequence variance decreases across experience. In (h–j, l), each dot is a mouse (n = 11 mice), and regression coefficients β and p-values (two-sided Wald test) are from linear mixed effects models with switch index as the fixed effect and mice as random effects. i) Mean licking position variance after the switch decreases across switch days. j) The mean reward-relative position of RR cell sequences is static across days. k) Distributions of peak firing positions on each switch day (fraction of place cells per animal, averaged across n = 11 mice, SEM omitted for clarity) for non-RR remapping cells (left), appearing cells (middle), and disappearing cells (right). Top row: by linear track position, converted to radians. Arrows, start of each reward zone. Bottom row: by position relative to the reward zone start. Horizontal dotted lines, expected uniform distribution for each day. Vertical gray dashed lines, reward zone start and surrounding ±50 cm. l) Both near ( ≤ 50 cm, top) and far from ( > 50 cm, bottom) the start of the reward zone, the fraction of place cells with disappearing fields decreases across experience. Non-RR remapping and appearing fractions did not show significant changes over experience.
