Divergent functional connectivity during attentional processing in Lewy body dementia and Alzheimer’s disease

Publication date: Available online 18 March 2017
Source:Cortex
Author(s): Xenia Kobeleva, Michael Firbank, Luis Peraza, Peter Gallagher, Alan Thomas, David J. Burn, John O'Brien, John-Paul Taylor
Attention and executive dysfunction are features of Lewy body dementia but their neuroanatomical basis is poorly understood. To investigate underlying dysfunctional attention-executive network interactions, we examined functional connectivity in 30 patients with Lewy body dementia, 20 patients with Alzheimer's disease, and 21 healthy controls during an event-related functional magnetic resonance imaging experiment. Participants performed a modified Attention Network Test, where they were instructed to press a button in response to the majority direction of arrows, which were either all pointing in the same direction or with one pointing in the opposite direction. Network activations during both target conditions and a baseline condition (no target) were derived by Independent Component Analysis, and interactions between these networks were examined using the beta series correlations approach.Our study revealed that functional connectivity of ventral and dorsal attention networks was reduced in Lewy body dementia during all conditions, although most prominently during incongruent trials. These alterations in connectivity might be driven by a failure of engagement of ventral attention networks, and consequent over-reliance on the dorsal attention network. In contrast, when comparing Alzheimer's disease patients with the other groups, we found hyperconnectivity between the posterior part of the default mode network and the dorsal attention network in all conditions, particularly during incongruent trials. This might be attributable to either a compensatory effect to overcome default mode network dysfunction, or be arising as a result of a disturbed transition of the default mode network from rest to task.Our results demonstrate that dementia syndromes can be characterized both by hyper- and hypoconnectivity of distinct brain networks, depending on the interplay between task demand and available cognitive resources. However these are dependent upon the underlying pathology, which needs to be taken into account when developing specific cognitive therapies for Lewy body dementia as compared to Alzheimer's.



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