Prefrontal and Occipital Network Excitability Differences in Dementia with Lewy Bodies and Alzheimer's Disease

Background There is a great need in distinguishing Dementia with Lewy Body (DLB) from Alzheimer's disease (AD) and elucidating its pathophysiology. Transcranial magnetic stimulation (TMS) evoked potentials (TEPs) offer a non-invasive measure of neurophysiological alterations associated with underlying disease pathology. Methods A total of 39 participants were included: 12 DLB, 10 AD, and 17 age-matched healthy controls (HC). TEPs were measured in the dorsolateral prefrontal cortex (DLPFC), primary motor cortex (M1), and primary visual cortex (V1). Results Global mean field potential (GMFP) TEP (130-250 ms) showed a significant interaction of group and stimulation site ( p = .0101, ηp 2 = 0.175) with a significant group effect ( p = .0071, ηp 2 = 0.234), attributed to higher GMFP in DLB compared to AD and HC in response to V1 stimulation ( p = .001, p = .001, respectively). TEP amplitude corresponding to P60 displayed a significant group*stimulation site interaction ( p = .0037, ηp 2 = 0.202) arising from differences in DLPFC stimulation, between DLB compared to AD ( p = .0013) and HC ( p = .0032). DLPFC N45 presented a significant stimulation site effect not associated to a specific group in addition to DLPFC N45 amplitude being correlated to the UPDRS-III score (r = 0.9, p = .0002). A relative higher left over right DLPFC P30 amplitude was correlated with poorer MoCA scores in AD (r = −0.84, p = .002), as indicated by others before. Conclusions DLPFC may be a target for both diagnosis and assessment of severity of motor symptoms in DLB and cognitive impairment in AD. These results propose a promising method to non-invasively distinguish DLB from AD and monitor disease, based on DLPFC and V1 network characteristics.