Chunk #33 — 3. Disruption of functional networks is associated with clinical impairment — 3.4 Neurobiological and clinical implications of network disruption
Important network differences have emerged from comparisons between PD, PDD and DLB, with an opposite EEG-pattern of connectivity associated with dementia onset (increased versus decreased connectivity). Interestingly, PDD and DLB changes were less severe though similar to those of AD with respect to the involvement of long-distance connections, although molecular in vivo and post-mortem studies do not support an Alzheimer's etiology.119,124 With regard to longdistance connections, hub regions may play a key role.125 Posterior parietal regions are among the brain regions with the highest connectivity, consistent with their role as multimodal association areas.126 Damage to heteromodal association hub regions, as seen prominently in AD,56,75 may prove particularly disruptive by dis-integrating unimodal and polymodal representations that normally converge at hubs after being processed in secondary and association cortices.126 In PD cognitive symptoms are generally milder than in AD, and pathology targets the motor circuits, whose damage may have more restricted effects on whole brain connectivity.49 Future studies will likely elucidate whether the relatively preserved cognition in PD is explained by the relative sparing of cortical hub regions until late disease stages.115
