We then computed the Spearman’s correlation between linear distance and either relative spike timing or gamma phase to determine how strongly these measures covaried. To determine the relationship between place field distance and correlation with gamma phase and spike timing, we divided the data into roughly four equally sized groups based on the distance

between place field peaks. We then computed the Spearman’s correlation between linear distance and either relative spike timing or gamma phase for each group. For quiescent SWRs, we used place fields recorded during the preceding behavioral session for pairwise decoding. To measure place field locations, we calculated an occupancy-normalized linearized place field for each cell

using 2-cm bins and smoothed IOX1 price with a 4 cm SD Gaussian curve. SWRs were excluded. A peak rate of 3 Hz or greater was required for a cell to be considered a place cell. Candidate replay events were defined as SWRs during which at least five place cells fired at least one spike each. We determined the sequential representation of position during a candidate replay event using a simple Bayesian decoder that has been described in detail before (Karlsson and Frank, 2009). Briefly, each event was divided into 15 ms bins and for each bin with at least one spike we calculated the spatial probability distribution using an uninformative prior. To determine whether the temporal sequence of decoded spatial probability distributions was a significant memory replay many we compared the regression BMS-354825 nmr of spatial locations with temporal bin to 10,000 regressions

in which the order of the bins was shuffled. The p value for each candidate event was defined as the proportion of the shuffled R2 values that was greater than the R2 value of the actual event, and an event with p < 0.05 was considered to be significant. Decoding was done with templates for both the animal’s current W-track and where applicable, the previously experienced W-track environment, in order to minimize false negatives. The R2 and the p value are correlated measures (Spearman ρ = −0.78). We focused on the p value measurement to quantify the improvement in coherence associated with significant replay events, although our results were similar when examined as a function of R2 values. To ask how gamma phase locking and coherence varied as a function of replay significance, we computed the phase locking and average coherence across significant and nonsignificant events. We used a permutation test to determine when the difference between significant and nonsignificant candidate events was significant. We compared the measured difference to the difference computed on 1,000 permutations of the p value associated with each candidate event. We thank members of the Frank laboratory, V. Sohal, S. Leutgeb, P. Janak, M. Brainard, and P. Sabes for comments on the manuscript. This work was supported by an NSF graduate research fellowship to M.F.C.