Fig. 7: Ketamine’s effect on the spatial coding of hippocampal place cells.

a A schematic illustration of in vivo calcium imaging via a miniaturized fluorescence microscope in CA1. Reproduced with permission from Sun and Giocomo⁹⁶. b Calcium event rate map of 4 example CA1 cells from 4 mice tracked across the experimental timeline shown on the top. Top, an example raster plot for one cell, where black lines are the animal’s trajectory and red dots are the location of each calcium event. Scale bar = 10 cm. c Mean calcium event rate comparison on baseline 1 (bsl 1) vs. baseline 2 (bsl 2), bsl 2 vs. ketamine (K), and bsl 2 vs. post-baseline (p-bsl) from all recorded neurons (4146 cells from 8 mice). Open circles are means across animals, filled dot is median across animals, and error bars are 25th and 75th percentiles across neurons. Ketamine decreases the mean calcium event rate both during (K) and after (p-bsl) drug treatment (p = 0.039 and 0.0078, respectively, two-tailed sign-rank tested on 8 mice). d, e Organized as in (c). Ketamine decreases the peak calcium event rate and spatial information of CA1 neurons (p = 0.0078 and 0.0078, respectively, two-tailed sign-rank tested on 8 mice). f Ketamine decreases the number of cells that qualified as place cell only during the drug day (p = 9.51 × 10⁻⁵, two-tailed paired t test). Each dot is one mouse. g Left, histogram of spatial correlations between sessions (2536 place cells from 8 mice). Right, spatial correlation per animal averaged over cells. Spatial correlation declines on bsl 2 vs. K compared to the correlation from the two baseline days (p = 0.0078, two-tailed sign-rank test on 8 mice). h Organized as in (g). There is no significant difference between the spatial correlation of bsl 2 vs. bsl 1 and bsl 2 vs. p-bsl (p = 0.38, two-tailed sign-rank test on 8 mice). i Spatial correlations averaged over all place cells per day. Ketamine consistently decreases spatial correlations compared to baseline sessions. Significant comparisons highlighted *p < 0.05, **p < 0.01, and ***p < 0.001. Source data are provided as a Source data file.