Spike-θ interactions in marmoset hippocampus.

(A) θ-index modulation are plotted as a function of the p-value on all recorded place cells revealed 6/289 significantly modulated place cells at p < 0.01 significance (p = 0.072, binomial test). Black dots indicate individual neurons, whereas red circles denote those units exhibiting statistical significance. (B). Shown are ACFs for the 3 units with the lowest p-values in panel A. A visible θ oscillation covarying with the HV ACFs computed is evident for each of these neurons. (C) PLV for each place cell, an indicator of θ-phase coherence, is plotted as a function of the p-value. Higher PLV indicates stronger coupling to a specific phase within the oscillation. A total of 18/269 place cells (with θ oscillations) exhibited HV θ-phase locking at p < 0.01 significance (p < 10⁻¹⁰, binomial test). Black dots indicate individual neurons, whereas red circles denote those units exhibiting statistical significance. (D) Cluster waveforms for the 3 most significant units from panel C are shown. (E) θ-phase firing distributions associated with the waveforms plotted in panel D. Note the position of each spike cluster in panel D corresponds to the position of the θ-phase distribution shown in panel E. θ-phase distributions were computed with 36° bins and were normalized to the bin with the maximum number of spikes. Panel E, lower right plots the preferred phase of all units with significant phase locking. (F) The LFP-based PLV index is plotted as a function of the p-value for each place cell. A total of 4/269 place cells were significantly modulated (p = 0.28, binomial test). Black dots indicate individual neurons, whereas red circles denote those units exhibiting statistical significance. Positive PLV indices indicate stronger phase coherence during HV locomotion and vice versa for negative PLV indices. For panels A, C, and F, significance was determined by empirical p-value computed on shuffled null-distributions. All p-values were computed one-sidedly, hence the lack of neurons exhibiting significant negative PLV-index in panel F. The underlying data can be found at https://doi.org/10.5061/dryad.kk63d49. ACF, autocorrelation function; LFP, local field potential; HV, high velocity; PLV, phase locking value.