Abnormal structures located chiefly in distal dendrites and, along with neurofibrillary tangles and SENILE PLAQUES, constitute the three morphological hallmarks of alzheimer disease. neuropil threads are made up of straight and paired helical filaments which consist of abnormally phosphorylated microtubule-associated tau proteins. It has been suggested that the threads have a major role in the cognitive impairment seen in alzheimer disease.