The projection pathways from the olfactory bulb to the secondary olfactory brain regions were equally highly correlated with neurofibrillary tangles and pathogenic proteins such as α-synuclein and hyperphosphorylated tau protein in these areas, which damage olfaction and contribute to the early pathogenic process of neurodegenerative diseases such as AD and PD. Here, MAPT is linked to neurodegenerative disease.