MAPT and proteostasis deficiencies: Strikingly, age‐related increases in PDE11A4 in the VHIPP ectopically accumulate in filamentous structures we term ghost axons due to increased phosphorylation of PDE11A4 at S117/S124 (PDE11A4pS117/pS124; Figures 1m, n and 4a–c), reminiscent of proteinopathies caused by hyperphosphorylation of tau (c.f., Kelly, 2018a).