MAPT and Cognitive impairment: We previously reported that no significant neurological deficits were observed in tau-/- mice on a Bl6/129sv mixed background (also created by Dawson et al.[13]) prior to 7 months of age, but that they subsequently expressed significant motor and cognitive deficits by 12-months of age, which were caused by toxic brain iron accumulation and associated disruption of dopaminergic pathways[5].