Photomicrographs showing activated Iba 1-ir microglia in the hippocampus of a 62-year old male chimpanzee (subject 20). Activated Iba1-ir microglia density (MGv, mm3) was significantly higher in CA3 compared to CA1 in the hippocampus of aged chimpanzees (a; * represents a significant difference, p = 0.01). Sex differences were not observed in activated Ibal-ir microglia density (b; p = 0.68). Whiskers represent 1 SD. Small circles represent outliers (1.5 × interquartile range). Hippocampal subfield CA1 (c–e) has significantly decreased microglial activation than subfield CA3 (f–h). Stratum oriens (so), stratum pyramidale (sp), stratum radiatum (sr). Scale bars = 250 μm (c–d, f–g) or 25 μm (e,h).