Fig. 7.

Hippocampal circuit mapping. A: DAPI-stained image of the hippocampus slice with the white rectangule marking the VSD imaging area shown in B and C. Overlay and alignment of DAPI staining with DIC living slice images located dentate gyrus (DG), CA3, CA2 (pointed by the arrowhead), and CA1. B: the space-time analysis indicating serial excitatory propagation in DG, CA3, and CA1. B: left: the background reference image with an analysis curve aligned with the hippocampal circuitry. The white arrowhead in the left panel points to the restricted photostimulation site (the blue spot) in the DG granule cell layer. B: right: the space-time map with the y-axis indicating the location along the analysis curve shown in the left panel (e.g., the pink, green, and yellow arrowheads correspond to the colored locations in the left panel) and with the x-axis denoting the time progression after the photostimulation. C: time frame series of the VSD response after photostimulation and a clear excitation flow through the hippocampal trisynaptic pathway. VSD signal amplitudes expressed as SD above the mean baseline signal are color coded. In this experiment, the map pixels with amplitudes ≥2 SD are plotted for analysis. The maps are identically color coded with warmer colors indicating greater excitatory activity. The white arrows in C point to the CA2 region, which had little activation.