Loss of EEG Network Efficiency Is Related to Cognitive Impairment in Dementia With Lewy Bodies

Abstract

Objective: The aim of this study was to test whether disturbed EEG resting-state functional connectivity and network organization are a potential neurophysiological substrate of cognitive impairment in dementia with Lewy bodies. Methods: EEG recordings were obtained in dementia with Lewy bodies patients, Alzheimer's disease patients and controls, matched for age and sex (N=66 for each group; 14 [21%] female; mean age: 70 years). We analyzed functional connectivity of band-filtered EEG time series using the phase lag index. Functional brain network topology was analyzed with the minimum spanning tree. Mini-Mental State Examination, Trail Making Test A, and Visual Association Test were used as cognitive measures. Results: Dementia with Lewy bodies patients showed lower connectivity strength in the alpha frequency band, compared to both controls and Alzheimer's disease patients (P<0.001). Functional network topology in dementia with Lewy bodies patients was less efficient and contained less hubs (P<0.01). Network characteristics in Alzheimer's disease patients were in between (but did not differ from) those of the other two groups. In dementia with Lewy bodies patients, lower alpha band phase lag index correlated with Visual Association Test scores and Trail Making Test scores (ρ=0.33 and ρ=0.31, respectively), whereas leaf fraction (a measure of 'network efficiency') correlated with Visual Association Test scores (ρ=0.29) and Mini-Mental State Examination scores (ρ=0.27). Conclusion: Functional networks of dementia with Lewy bodies patients are characterized by decreased connectivity strength and a loss of network efficiency and hubs. Severity of these disturbances is related to cognitive impairment, suggesting that network disturbances mediate between neuropathology and the clinical syndrome in dementia with Lewy bodies.