Effective connectivity abnormalities in Lewy body disease with visual hallucinations

Area of Science:

• Neuroscience
• Neurology
• Cognitive Science

Background:

• Visual hallucinations (VHs) are a common and distressing symptom in neurodegenerative diseases like Dementia with Lewy Bodies (DLB), Parkinson's Disease (PD), and Parkinson's Disease Dementia (PDD).
• The underlying neural mechanisms, particularly alterations in brain network connectivity, remain incompletely understood.

Purpose of the Study:

• To investigate the changes in effective connectivity within the visual network (VIS) and dorsal attention network (DAN) associated with VHs.
• To compare connectivity patterns in patients with and without VHs across DLB, PD, and PDD.

Main Methods:

• Utilized transcranial magnetic stimulation-electroencephalography (TMS-EEG) to measure cortical activation.
• Stimulated key regions of the DAN, including the intraparietal sulcus and frontal eye fields.
• Compared TMS-evoked responses in patients with VHs (n=11) versus those without VHs (n=15).

Main Results:

• Patients with VHs exhibited lower TMS-evoked cortical activation within the DAN after stimulation of the intraparietal sulcus and frontal eye fields compared to patients without VHs.
• No significant differences in activation were found based solely on cognitive impairment status.
• In patients with cognitive impairment, VHs correlated with reduced activation following intraparietal sulcus stimulation.

Conclusions:

• Patients with DLB, PD, and PDD experiencing VHs demonstrate reduced effective connectivity of the right intraparietal sulcus within the DAN.
• This study provides initial evidence linking VHs to specific intraparietal sulcus dysfunction within the DAN in these patient populations.