To answer this question, in a within-subject, placebo-controlled, double-blind, cross-over study the cholinergic system was manipulated by protracted oral administration of rivastigmine—a cholinesterase inhibitor, which is widely used for the treatment of cognitive deficits in Parkinson’s disease (see STAR Methods for details and Table S2 for the testing schedule). Here, BCHE is linked to Cognitive impairment.