APOE and Parkinson disease: This is consistent with evidence in the Alzheimer and Parkinson disease literature, where a functional alteration of the DMN is already present in APOE4+ cognitively normal individuals and in cognitively unimpaired Parkinson disease patients, respectively.[34,35] It is also important to note that we defined cognitive impairment conservatively as failure on at least 3 tests rather than failure on 1 or more tests.