MAPT and Alzheimer disease: Pamphlett et al. have detected LC neurons filled with environmental toxins and heavy metals with variable concentrations in the human brain (Pamphlett, 2014; Pamphlett and Kum Jew, 2014; Pamphlett et al., 2020), yet in human AD the population of LC neurons enriched in heavy metals were not the same as those enriched in hyperphosphorylated tau (Pamphlett and Kum Jew, 2015).