48. Fmri for study of brain resting state networks in patients with degenerative brain diseases

Resting-state networks (RSNs) are characterized by organized basal activity during rest and by low-frequency signal fluctuations that can be studied by fMRI. To date, several RSNs have been consistently reported, including the task-positive networks (e.g., the primary motor, visual and auditory network, the left and right fronto-parietal RSNs, and the extrastriate visual RSN) and the default mode network (DMN). Functional connections of these RSNs tend to be strongly related to structural white matter connections, suggesting the existence of an underlying structural core of functional connectivity networks in the human brain. Several hundred studies are now available that address integrity of resting connectivity in patients with Alzheimer’s disease (AD) and mild cognitive impairment (MCI), as well as preclinical at-risk subjects. Most studies focus on the default mode network (DMN), a system of specific brain areas showing strong connected resting activity that attenuates during goal-directed behavior. The extent of intrinsic brain activity tends to be strongly correlated with cognitive processes and is specifically disrupted in AD and MCI patients and at-risk subjects, with changes seeming to evolve during the transition between the disease stages. Regarding Parkinson’s disease (PD) and PD with cognitive impairment the data on changes in the DMN and other RSNs remain rather conflicting and are probably related to the phenotypic and pathological heterogeneity of the disease. The DMN disturbances in PD may be linked both to the dopamine deficiency (that can be at least partially reversed by dopaminergic medication) and to cognitive dysfunctions. The lecture will focus on the DMN and other RSNs results as assessed by fMRI, particularly in PD and early AD. The impact of dopaminergic and cholinergic medication will also be discussed.