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. Author manuscript; available in PMC: 2021 May 21.
Published in final edited form as: Neuron. 2016 Sep 1;91(6):1342–1355. doi: 10.1016/j.neuron.2016.08.008

Figure 1. Overview: Heterogeneity of Ripples in CA1, CA2, and CA3 Regions.

Figure 1.

(A) Histological section parallel to the transverse axis of the hippocampus double stained with DAPI (blue) and anti-PCP4 (green) to identify the CA2 region. The cartoon of the electrode shanks is constructed following the track marks visible on the inset.

(B) Example peri-SPW-R firing histograms of CA1-CA2-CA3a, b, and c pyramidal cells, triggered by the SPW troughs. Histograms are color coded to mark their regions of origin. All histograms are remarkably similar with the exception of a subpopulation of CA2 cells. CA2 boundaries are marked with dashed lines. An example CA1 SPW-R used as trigger is shown in green. Arrows illustrate the expected propagation of synchronous unit firing during SPW-Rs based on the anatomy. From CA2, excitation propagates to CA3a, b, and c and then to CA1. Alternatively, CA2 activity can also propagate directly to CA1 (dashed line).

(C) Upper panel: LFP-CSD map triggered by one CA2 ripple (white arrow). Note the characteristic negative SPW (black lines) and sinks in the str. radiatum (in blue, marked by arrow) accompanied by ripples (black lines) and flanked by passive sources in the pyramidal layer and str. lacunosum-moleculare (red) after the CA2 ripple peak. Bottom panel: Another characteristic pattern triggered by CA2 ripple (white). Excitatory currents in CA1 in str. oriens (blue sinks and black negative waves, black arrow) were accompanied by return currents in str. radiatum (red sources). Note ripples in all CA1 pyramidal layer sites. See also Figure S1.