Figure 11.
Pyramidal leads interneuronal cell firing at cortical ripple peaks. A, Superior temporal gyrus granular/supragranular layer ripples detected during NREM in a Utah Array recording. Top, Average broadband LFP. Middle, Average time-frequency. Bottom, Single-trial example trace in broadband LFP (black) and 70-100 Hz bandpass (blue, left represents analytic amplitude; right represents sweep). B, Mean broadband LFP locked to cortical ripple centers (black) and associated local PY (blue; N = 69) and IN (red; N = 23) spike rates during NREM. C, Circular mean 70-100 Hz phase of spikes of each PY (N = 47, mean = 2.97 rad, p = 5 × 10−21, Rayleigh test) and IN (N = 22, mean = 3.25 rad, p = 3 × 10−13) during local cortical ripples (minimum 30 spikes per unit). PY spiking preceded IN spiking by 0.28 rad (p = 0.02, Watson–Williams test). The 0 rad corresponds to the trough, and π rad corresponds to the peak of the ripple. D, Circular mean ripple phase-lags of spikes from each PY (N = 47) to each IN (N = 22) (N = 1034 unit pairs, mean = 0.31 ± 0.63 rad, p = 4 × 10−51, one-sided one-sample t test). E, Pyramidal Interneuron Network Gamma ripple generation mechanism consistent with single-unit recordings, animal studies (Stark et al., 2014), and modeling (Buzsáki and Wang, 2012). Abrupt depolarization causes synchronous PY and IN firing, which then spike rhythmically, separated by fixed intervals because of recurrent inhibition. F, Pairs of PYs (PY–PY) cofire ∼7 times more often within 5 ms of each other during ripples compared with randomly selected epochs in between ripples matched in number and duration to the ripples. Similarly, PY–IN pairs cofire ∼10 times more during ripples. IN, Putative interneuron unit; PY, putative pyramidal unit.