Figure 7.

Remapping is not associated with changes of spatial firing patterns within recording sessions nor adjustments of tetrode position. A, As a control to assess whether maps are stable within the sessions that occurred on remapping days, spatial correlation scores were calculated in two ways: (1) as in Figure 6D, between Training Session 1 and Training Session 2 on each day (“between sessions”); and (2) as a control, between the first and second half of each training session (excluding the first five laps in each direction with no eyeblink stimuli; “within sessions”). These values are reported independently for spatially stable and remapped days of the experiment. For spatial correlation scores calculated between sessions (left bars), on spatially stable days the average value was 0.792 ± 0.02 (n = 12 rats), and on remapped days it was 0.073 ± 0.015 (n = 6 rats). These values correspond to the mean of the average spatial correlation scores of each cluster in Figure 6D and were significantly different from each other (Wilcoxon Signed Ranks Test: Z = −2.201, p = 0.028). For the control, spatial correlation scores calculated within sessions (right bars), the average value on spatially stable days was 0.769 ± 0.019 (n = 12 rats), and on remapped days it was 0.707 ± 0.038 (n = 6 rats). These values are not significantly different (Wilcoxon Signed Ranks Test: Z = −1.572; p = 0.116). Therefore, spatial firing patterns are no less stable within remapped sessions compared to spatially stable sessions. B, Typically, the depth of two or three tetrodes (of a total of 12 tetrodes) was adjusted (or “turned”) per rat per day of the spatial eyeblink experiment. C, D, To address the possibility that tetrode depth adjustment might elicit recording instability that could account for remapping, the number of tetrodes that underwent depth adjustment was calculated for days preceding spatially stable CA1 maps (C, 327 days of experiment) versus days preceding remapping (D, 29 days of experiment). Tetrodes were never turned immediately before recording sessions, and relatively few tetrode adjustments were made on the majority of days that preceded remapping.