Figure 2. Preferred theta phase of spikes during REM sleep depends on the position of the soma in the CA1 pyramidal layer.

a, Preferred theta phase for each neuron (dots) recorded at different depths of the layer during REM sleep. Solid lines; mean (± 95% confidence intervals) preferred theta phase (green, REM). For comparison, the mean preferred theta phase during RUN (gray) is also shown. The few neurons above and below recording sites 3 and 3 were added to values at 3 and 3, respectively. b, Distribution of the preferred theta phase of pyramidal cells in the superficial (recording sites above 0), middle (site 0) and deep (sites below 0) depths during maze running (RUN) and REM sleep. Note unimodal distribution of theta phase preference in the deep layer group during RUN and bimodal distribution during REM sleep. Top gray traces, idealized reference theta cycle in CA1 pyramidal layer. c, Distribution of preferred theta phases during RUN and REM sleep. Only neurons which showed significant theta phase modulation during both RUN and REM sleep are included here. Top and right: theta phase preference histograms for REM sleep and RUN. Note bimodal distribution of preferred theta phase during REM sleep. Neurons with < 120° or > 300° preferred theta phases during REM (magenta) were designated as REM-shifting cells, while those between 120° to 300° (light blue) as non-shifting cells. d, Left, depth distribution of REM-shifting and non-shifting neurons (± 95% Clopper-Pearson confidence intervals). Right, distribution of the fraction of REM-shifting cells as a function of depth in the pyramidal layer. e, Percent of neurons with > 90° phase shift between RUN and REM (± 95% Clopper-Pearson confidence intervals) in different regions. EC2, EC3, EC5 correspond to neurons in layers II, III and V of the entorhinal cortex, respectively. Interneurons did not shift phase preference across states. Theta phase of LFP recorded from the CA1 pyramidal cell layer was used for all the cell types.