P 143 Diverse functional connectivity patterns in Lewy body dementia and Alzheimer’s disease during attentional processing

Abstract

Introduction Patients with Lewy body dementia typically suffer from symptoms of parkinsonism, visual hallucinations and fluctuating cognition with a pronounced attentional impairment. However, the underlying network dysfunctions of the latter are unclear, which obstructs applying targeted cognitive therapies. Therefore we aimed to study network interactions during attentional processing in Lewy body dementia and compare them with Alzheimer”s disease and healthy controls. Subjects and methods 30 patients with Lewy body dementia, 20 patients with Alzheimer’s disease and 21 matched healthy controls performed a modified version of the Attention Network Test within an MRI scanner. They were asked to press a button in reaction to the majority direction of four displayed arrows which could either point into the same direction (congruent condition) or with one arrow pointing to the opposite site (incongruent condition). The resulting event-related fMRI data were preprocessed and then decomposed into functional networks using an Independent Component Analysis. We visually chose five networks (executive network, ventral and dorsal attentional network, default mode network) for an in-depth analysis of their interactions. Then we extracted timeseries of each network applying dual regression. Beta estimates were calculated by performing GLMs using each event as a separate regressor. They were grouped together as beta series for similar events and correlated with each other. Networks with positive correlations were assumed to have similar patterns of inter-trial variability as an indication of functional connectivity. These network interactions could be then compared between groups. Results We found reduced functional connectivity of ventral and dorsal attention networks in patients with Lewy Body dementia in contrast to patients with Alzheimer’s disease and healthy subjects, particularly during incongruent trials. Contrarily, in Alzheimer”s disease, we could observe increased connectivity between the posterior part of the default mode network and the dorsal attention network, which was also most prominent during incongruent trials. Discussion We assume that the reduced connectivity of attention networks in Lewy body dementia is a result of a disturbed bottom-up transfer from ventral attention networks, whereas the hyperconnectivity between the default mode network and the dorsal attention network in Alzheimer”s disease might constitute a compensational mechanism to overcome default network dysfunction or relate to an inefficient transition of the default mode network from a resting state to a task-related state. In brief, dementia syndromes can be composed of both hyper- and hypoconnectivity of brain networks, depending on the interplay between given neural resources, cognitive requirements and also the underlying pathology.