Ricerc@Sapienza

Visual hallucinations (VH) are particularly frequent in Parkinson's disease (PD), PD with dementia (PDD) and Dementia with Lewy bodies (DLB). Beside parkinsonism, the clinical features of PDD and DLB crucially include visual hallucinations and cognitive impairment. VH in PD, PDD and DLB typically progress along a clinical spectrum ranging from vivid dreams to frank psychosis, which is associated with the development of dementia and institutionalization. Understanding mechanisms of VH is crucial in detecting new targets for novel therapeutic approaches in patients with VH. The brain mechanisms underlying VH in PD, PDD and DLB are largely unclear. VH might reflect a failure in recruiting the dorsal attentional network (DAN) during periods of conflict resolution in visual processing. The DAN is composed of widespread neural circuits including regions within the frontal eye fields (FEF), and the intraparietal sulcus (IPS) in the right hemisphere. Transcranial magnetic stimulation (TMS) is a neurostimulation technique able to assess brain functions and disease-associated dysfunction. Recently introduced combined TMS-EEG approaches would provide an interesting window in the investigation of abnormal brain dynamics responsible for VH. In this study, we will use TMS-EEG to investigate excitability and connectivity abnormalities in each of the single nodes within the DAN (FEF and IPS) and the visual cortex, in patients with VH and in age-matched healthy subjects. Finally, given the pathophysiological role of decreased cortical cholinergic transmission in patients with VH, we will also assess the link between changes in the DAN network connectivity and changes in short-afferent inhibition (SAI), a non-invasive TMS measure of the cortical cholinergic tone.