For example, in a recent study in PD patients combining MRI with cholinergic PET, only a weak-to-moderate relationship (r = 0.29) was found between the posterior basal forebrain volume (mainly corresponding to the NbM) and cortical acetylcholinesterase activity.59 Furthermore, in the same study, the two cholinergic markers were found to contribute differently to different cognitive functions. This evidence concerns the gene ACHE and Parkinson disease.