Chronic Neuropixels probe recordings across mPFC subregions.

(a) Left: an image of the Neuropixels probe, right: the probe mapping from one example animal where a part of the trace is seen going through the hippocampus (top) and mPFC (bottom). (b) An example segment of data with the animals running speed (top) and spiking activity recorded from the hippocampus, dorsal mPFC and ventral mPFC (top to bottom). (c) An overview of the behavioral task. Each day starts with a period of rest, followed by rule learning in the maze, interleaved with short periods of rest and the day ends with a period of rest or sleep of up to 60 minutes. Four different rules have to be learned over the course of multiple days, based on allocentric and cue-based strategies. (d) The number of sorted neurons per session for each (sub-)region. The different markers indicate different animals.

A subset of neurons in the mPFC is modulated by hippocampal SWRs and theta phase.

(a) Six example neurons in the mPFC that are SWR-excited (top), SWR-inhibited (middle) and SWR-unmodulated (bottom; dorsal mPFC in olive, ventral mPFC in blue). (b) The average normalized firing rates of all SWR-excited and SWR-inhibited neurons in the dorsal and ventral mPFC. Data is presented as mean of all neurons ± SEM. (c) The mean of the SWR modulation per subregion during periods of exploration in the maze. (d) The percentage of neurons that is SWR-excited (solid fill) and SWR-inhibited (dashed fill) per mPFC subregion. (e) The mean overall firing rates per subregion of SWR-excited (solid fill), SWR-inhibited (dashed fill) and SWR-unmodulated (no fill) neurons in the maze. (f) The percentage of neurons that is phase-locked to hippocampal theta per brain region. (g) The percentage of neurons that is phase-locked to hippocampal theta, divided between mPFC neurons that are SWR-excited (solid fill), SWR-inhibited (dashed fill) and SWR-unmodulated (no fill). (h) Left panels: the mean angle (−π to π) and R̅ (0.0 to 0.6) for all dorsal mPFC clusters that were significantly phase locked to hippocampal theta, divided between SWR-excited clusters (top), SWR-inhibited clusters (middle) and SWR-unmodulated clusters (bottom). Middle panels: the mean angle and R̅ for all phase locked clusters in the same configuration as the left panels, but for the ventral mPFC. Right panels: histograms of the mean angles of all theta phase-locked clusters that were SWR-excited, SWR-inhibited or SWR-unmodulated (top to bottom). p-values indicate the result of a Kolmogorov-Smirnov test to test the difference in distribution between the dorsal (olive) and ventral (blue) mPFC.

SWR-unmodulated neurons are spatially tuned, directionally selective and show theta cycle skipping.

(a) The firing patterns of eight example neurons in the maze, showing a range of spatial tuning scores (in bits/spike) sorted from highest to lowest. (b) Left panel: the spatial tuning score per subregion. Right panel: the spatial tuning score per subregion divided between mPFC neurons that are SWR-excited (solid fill), SWR- inhibited (dashed fill) and SWR-unmodulated (no fill). (c) Three example trials where the head directions are categorized as future choice or alternative choice, North or South, and left or right. (d) Left panel: the percentage of neurons that fire significantly higher than the shuffled population for at least one of the head direction categories. The chance level is indicated at 15%, as an alpha of 0.05 was maintained for each of the three direction categories (future versus alternative, North versus South, and left versus right). Right panel: the absolute maximum directional selectivity index per subregion for mPFC neurons that are SWR-excited (solid fill), SWR-inhibited (dashed fill) and SWR-unmodulated (no fill). (e) Spike time auto-correlations of two example neurons where the peak of the smoothed signal (in black) at 250 ms is subtracted from the peak at 125 ms and normalized to the highest of the two peaks to obtain the cycle skipping index (left panels). To determine the statistical significance, the score is compared to a shuffled population (right panels). (f) Left panel: the percentage of neurons that showed significant theta cycle skipping properties per subregion. Right panel: the theta cycle skipping index per subregion divided between mPFC neurons that are SWR-excited (solid fill), SWR- inhibited (dashed fill) and SWR-unmodulated (no fill).

Non-local representations in the mPFC are predictive of the animals’ upcoming choice.

(a) Three examples of trials where the decoded positions (grey scale) and real positions (red) are shown per maze segment. Predictive and non-predictive segments are shown in light and dark brown spans at the top. (b) The prediction index per session based on the decoded non-local representations while the animal was at the start of the maze, separated for when the rule was not yet learned and when the rule was learned, and for the allocentric (navy) and cue-based (orange) rules. Shown in light grey is the prediction accuracy based on the shuffled decoded posteriors, and p-values indicate the result of a Wilcoxon signed-rank test between the real and shuffled predictions. (c) Left panel: an example learning curve (in black) with a rule switch from South to North after 10 trials, and the predicted directions based on the non-local representations overlayed (navy). Right panel: the lag (in number of trials) between the real direction and decoded direction per session for allocentric (navy) and cue-based (orange) strategies. A negative lag indicates that the decoded direction preceded the real direction over the course of learning. P-values indicate the result of a one-sample Wilcoxon test to test the deviation from zero. (d) The percentage of timepoints of representations in the hippocampus that were local, predictive of the upcoming choice or predictive of the alternative choice, during mPFC local representations (left panel), during mPFC representations of the alternative choice (middle panel) and mPFC representations of the upcoming choice (right panel). (e) The overlap between representations in the same configuration as in (d), but for mPFC representations occurring during hippocampal local representations (left panel), during hippocampal representations of the alternative choice (middle panel) and hippocampal representations of the upcoming choice (right panel).

Non-local representations in the mPFC are not linked to hippocampal SWRs and theta phase.

(a) The occurrence of representations of alternative choice (left) and upcoming choice (right) in the mPFC in temporal proximity to hippocampal SWRs. (b) The firing rates of mPFC neurons that are SWR-excited, SWR- inhibited and SWR-unmodulated, during representations of upcoming and alternative choices, normalized to the average firing rate at the start of the maze. (c) A histogram of the phase of hippocampal theta oscillations at which the start of each representation of upcoming and alternative choices in the mPFC occurred. (d) The phase locking score (Rayleigh’s Z) of representations of upcoming and alternative choices to hippocampal theta oscillations compared to a randomized population.

Non-local representations in the hippocampus are linked to SWRs and theta phase.

(a) The occurrence of representations of alternative choice (left) and representations of upcoming choice (right) in the hippocampus in temporal proximity to SWRs. (b) The firing rates of mPFC neurons that are SWR-excited, SWR- inhibited and SWR-unmodulated, during representations of upcoming and alternative choices, normalized to the average firing rate at the start of the maze. (c) A histogram of the phase of hippocampal theta oscillations at which the start of each representation of upcoming and alternative choices in the hippocampus occurred. (d) The phase locking score (Rayleigh’s Z) of representations of upcoming and alternative choices to hippocampal theta oscillations compared to a randomized population. Due to less multi-unit activity recorded in the hippocampus, fewer sessions were available with good decoding quality, and figure is made with N=12 sessions from 3 animals.