Fig. 2: 4-Hz and theta oscillations in the mPFC, HPC, and PPC during spatial learning.

a Upper panel: example of LFP recorded simultaneously from the mPFC, HPC, and PPC during training in the Barnes maze. Middle: magnification of segments of LFP recordings showing theta (left) and 4-Hz oscillations (right). Lower panel: spectrograms for LFP recordings shown in the middle panel. b Example of spectrogram of an LFP recorded from the mPFC comparing theta and 4-Hz spectral energy across time, and comparison of instantaneous energy of 4-Hz and theta frequency bands aligned with the instantaneous speed. Gray areas are periods of locomotion (instantaneous speed over 4 cm/s). c Upper panel: z-scored colorplot of energy of theta oscillation in turn to peaks of 4-Hz oscillation in the mPFC (left), HPC (middle), and PPC (right) for all training sessions. Lower panel: average theta z-scored energy in turn to 4-Hz peaks. Note that theta energy is minimal when 4-Hz reaches the maximum energy. Data are presented as mean (solid line) ± SEM (shaded area). d Box plot comparing the mean z-scored spectral power of the 4-Hz and theta oscillations in the mPFC (left), HPC (middle), and PPC (right) with respect to mobility (M) and immobility (I) episodes. For the box plots, the middle, bottom, and top lines of the box plot correspond to the median, lower, and upper quartiles, and the edges of the lower and upper whiskers correspond to the 5th and 95th percentiles. *P < 0.05; **P < 0.01 ***P < 0.001; Sidak’s multiple comparisons test after two-way ANOVA.