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. Author manuscript; available in PMC: 2015 Jul 16.
Published in final edited form as: Neuron. 2014 Jul 16;83(2):467–480. doi: 10.1016/j.neuron.2014.06.023

Figure 2. Local Activation of Pyramidal Cells Induces High-Frequency Oscillations.

Figure 2

(Aa) Schematic of three diode-probe shanks overlaid on a confocal image of ChR2 expression in CA1 pyramidal cells (CaMKII, red; EYFP, green; DAPI, blue; pyr, CA1 pyramidal layer).

(Ab) Spontaneous ripple and iHFOs recorded by the same electrode (freely moving CAG::ChR2 rat; single-shank illumination; peak light intensity at the middle of the CA1 pyramidal layer: 0.11 mW/mm2). Right: time-frequency decomposition (average of n = 458 spontaneous or n = 10 induced events).

(Ac) HFOs induced in a freely moving CaMKII::ChR2 mouse (0.14 mW/mm2). Right: time-frequency decomposition (n = 367 spontaneous or n = 20 induced events).

(Ad) Prolonged illumination (400 ms light pulses; n = 20) induces oscillations that decrease in frequency and amplitude (same recording site as in [Ac]).

(B) Ripple power and frequency increase with SPW amplitude.

(Ba) Left: depth profile of averaged sharp-wave ripples in a freely moving mouse (n = 961 events; vertical site separation: 100 μm). Voltage traces (light gray) are superimposed on current-source density (CSD) map. Black trace: site of maximum amplitude ripple; heavy gray trace: site of maximum amplitude SPW. pyr, pyramidal layer; lm, str. lacunosum-moleculare. Right: examples of lower (top) and higher (bottom) amplitude SPWs recorded from the same mouse.

(Bb) Ripple power and frequency increase with SPW amplitude (colored bands correspond to n = 26 experiments in four freely moving mice equipped with 32-site linear probes; bands: mean ± SEM over ripple events). Numbers indicate median rank correlation; ***p < 0.005, Wilcoxon’s signed-rank test.

(C) iHFO power and frequency increase with light intensity.

(Ca) Left: traces during individual pulses (50 ms), plotted versus light intensity at the middle of the CA1 pyramidal layer. Right: time-frequency decomposition (n = 20 induced events). Weaker light only induces spiking, whereas oscillations of increasing amplitude and frequency are induced with stronger light.

(Cb) Power and frequency (scaled by the properties of the same-site spontaneous ripples; bands: mean ± SEM, n = 10 experiments in four freely moving CaMKII::ChR2 mice) increase with light intensity.