Network based statistics shows that rem sleep behavior disorder and visual hallucinations increase functional connectivity in early dementia with Lewy bodies

Dementia with Lewy Bodies (DLB) is a heterogeneous disease characterized by four core clinical features, namely visual hallucinations, REM sleep behaviour disorder (RBD), cognitive fluctuations and parkinsonism. In this paper, we perform for the first time a comprehensive study on the relationship between all these features and functional connectivity derived from high-density electroencephalographic data. To quantify functional connectivity, we used two different connectivity metrics, each one averaged on individual theta and alpha frequency bands. The latter were defined by determining the individual theta-to-alpha transition frequency through a previously validated package called transfreq. The study was performed using a cohort comprising 33 subjects affected by early stage DLB (mean age 82 {+/-} 6 years, males/females: 23/10) and 21 healthy controls (mean age 71 {+/-} 9 years, males/female: 10/11). After showing that overall DLB determines a shift toward lower frequencies of posterior dominant rhythm and theta-alpha transition, we used Network Based Statistic (NBS) to explore differential connectivity networks between subgroups of DLB patients with different core features. We consistently found that the presence of both visual hallucinations and RBD is associated with increased connectivity in early DLB patients mostly in the left hemisphere, while cognitive fluctuations and parkinsonism appear to have a non-significant impact on functional connectivity metrics. These findings may represent an initial compensatory mechanism in response to underlying neurodegeneration.