MAPT and Cognitive impairment: Single-molecule array (SIMOA) and xMAP technology determined that Aβ42 levels, which are positively correlated with CSF Aβ42 levels but negatively correlated with the CSF t-tau levels, were higher at the mild cognitive impairment (MCI) stage than the AD stage, and the t-tau levels were positively associated with the burden of brain tau deposition on tau PET across the AD spectrum; i.e., the Aβ42 levels are elevated during the MCI stage and reach a plateau prior to the demented stage, whereas the t-tau levels increased with AD-associated tau pathology 150, 151.