This study is looking at how probiotics might help with Rapid Eye Movement (REM) sleep behavior disorder (RBD) in people with Parkinson's disease (PD). RBD is a condition where people act out dreams, and it's linked to PD. The study will use different kinds of pictures of the brain, called multimodal imaging, to see changes before and after taking probiotics. They'll also check things like blood and stool for chemicals like glutamate and GABA, which are important for brain function.

• Participants must be between 40 and 80 years old.
• No major changes in medication or probiotic use two months before joining.
• The study involves tests like MRI scans and blood samples.

This research might help us understand if probiotics can improve sleep and movement issues in PD. Eligible participants will need to comply with these criteria and provide informed consent.