We sought to ensure that the higher cross correlation values were not the result of more place fields in the choice arm resulting in a lower average difference between field centers of HPC-LS matched pairs. We first decided to determine if there was a difference in the average distance between LS and HPC place field pairs for the forced side, central stem, and choice side. We found that there was no significant difference between the average distance between LS and HPC pairs in the forced arm versus choice arm (two-tailed two sample t-test, t(67) = 1.8, p>0.05), so the proximity of HPC-LS pairs did not account for the difference in cross correlation values for forced vs. choice sides. There was a small (3cm) but significant (two-tailed two sample t-test, t(51) = 2.2, p=0.03) difference in distances when comparing the choice side to the middle stem. (Running a one way anova with all three values, F(3,83) = 3.24, p = 0.04). To further ensure that distance between pair centers was not causing the increase cross correlation in the choice arm, we subsampled the data. We found that eliminating the very closest pairs (pairs that had centers within 3cm of each other) was more than sufficient to result in an insignificant difference between forced, choice, and middle pair distances (one way anova F(3,84) = 1.92, p>0.05, with both t-tests also p>0.05). When subsampled as described, the average cross correlation for pairs on the choice side was still significantly higher than the average in either the forced side or middle stem (double sided t tests, t(51) = 1.96 p<0.05 for comparing forced to choice and t(51) = 2.2 p<0.05 for comparing central to choice). (A) The average cross correlations of subsampled data. (B) All cross correlations of subsampled data.