Age-related impairment of paravascular CSF recirculation was evaluated 30min after intracisternal injection of small molecular weight CSF tracer Texas Red-conjugated dextran (MW 3kD, Dex-3) and large molecular weight ovalbumin-conjugated ALEXA 647 (MW 45kD, OA-45). Representative saggital and coronal slices from young (A) and old (B) brains show marked reduction in CSF tracer penetration throughout the aged compared to the young brain. CSF tracer penetration within defined brain regions was evaluated and heat maps from anterior (C) and posterior (D) slices depict the change in mean OA-45 CSF tracer penetration observed in each region between old and young brains. Quantification of OA-45 penetration in different regions showed that paravascular CSF recirculation was significantly impaired in the lateral and ventral cortex of both the anterior and posterior slices (*P<0.05, **P<0.01, ***P<0.001, Young vs. Old; 2-way ANOVA; n = 4 per group).