AA-containing PCs are localized in the cell layers in the hippocampal formation. High-magnification IMS at a raster size of 15 μm (C, E, and G), and successive section stained with HE (A) revealed that AA-containing PCs were enriched in the cell layer regions of the hippocampal formation, which are the pyramidal cell layer of CA1 and the granule cell layer of DG, whereas PC (16:0/16:0) was widely distributed in the dendritic region of the hippocampal formation (B). D, F, and H: merged images. The relative abundance of the 2 ions is indicated in the color scale bar.