Figure 6. Phase preference of neuron spikes during induced firing and LFP theta oscillations.
(A) Non-local INT tend to spike at the trough of theta-band chirp pattern PV activation. a, PYR-PV network recorded in CA1. One PYR and one PV are shown for each of two shanks, 400 μm apart. Auto- and cross-correlation histograms (calibration: 10 ms, 50 coincident counts) during spontaneous spiking (no-light condition) indicate mono-synaptic connectivity of the same-shank PYR-PV pairs, zero-lag synchronization between the PV pair (on shanks 2 and 4), and time-shifted temporal correlation between cross-shank PYR-PV pairs. b, Top: during chirp-pattern PV activation on shank 2, the local PV spikes in-phase with the chirp, whereas the non-local PV spikes anti-phase; the inverse occurs during PV activation on shank 4 (bottom). c, During PV activation in CA1, PV recorded on the illuminated shank spike at peak of theta-band light stimulation whereas non-local INT tend to spike around the trough. PYR emit spikes near the trough. Circular-linear correlation coefficients are shown; **: p<0.01, χ2 test. (B) Top panels, spiking frequency-phase maps of CA1 units during chirp-pattern PV activation. Only light-modulated units are included (p<0.05, permutation test). Middle panels, spiking gain maps of CA1 units during LFP theta; only theta-band modulated units are included (p<0.05, Rayleigh test). Bottom, phases for cells modulated by the chirp in the theta band and by LFP theta oscillations (both states: 24 PV, blue; 24 PYR, red; light dots, cells significantly modulated by either chirp or LFP theta). Circular-circular correlation coefficients are shown. Marginals show the mean firing rate (scaled 0–1 for each unit) during the two states (thin lines show marginals for cells modulated only in one state). (C) Diagram summarizing the spiking phases of CA1 neurons during LFP theta (local LFP, bottom) and during theta-band chirp-pattern PV-activation (top). During theta-band PV-activation, locally-driven PV cells follow the drive closely. Non-local cells spike at the opposite phase of the light-driven PV spikes. See also Figure S6.