MAPT and Alzheimer disease: More recent immunohistochemical and biochemical studies done in our laboratory and elsewhere focusing on the frontal cortex, have found that the tau in the brains of those with AD who suffered with psychosis is hyperphosphorylated relative to those who did not, significant as tau phosphorylation is widely believed to be a critical event in the formation of neurofibrillary tangles [21, 22].