The investigators aim is to study neuropsychiatric symptoms and underlying abnormalities in resting-state fMRI in patients with Parkinson's disease (PD) suffering from neuropsychiatric fluctuations, to enhance the understanding of the pathophysiological mechanisms underlying neuropsychiatric symptoms.

Parkinson's disease (PD) is primarily classified and known as a movement disorder characterized by tremor, bradykinesia and rigidity. However, clinical examination and research have shown that PD extensively affects other systems as well, giving rise to non-motor symptoms (NMS) such as anxiety, sleep disorders, apathy, depression, cognitive impairment, and hallucinations. These non-motor fluctuations (NMF) represent a main source of disability in PD and among those, neuropsychiatric fluctuations are the most frequent. During the dopaminergic OFF-drug state anxiety, apathy, and depression are common, whereas during the dopaminergic ON-drug state euphoria, well-being, impulse control disorders (ICD) and other behavioral addictions, mania, and psychosis might occur.

Despite the severe consequences associated with dopaminergic modulation, the understanding of the pathophysiological mechanisms of neuropsychiatric symptoms is still limited and better detection and more effective treatments are needed. Fluctuating PD is a very powerful model allowing to study opposite psychiatric states intra-individually in both levodopa dopaminergic ON- and OFF-drug state, allowing to abstract many interpersonal variables.

Neurotechnology and advanced neuroimaging techniques can improve the understanding of the neural basis and brain mechanisms of specific neuropsychiatric symptoms in PD. In particular, dynamic functional connectivity (FC) analysis characterizes functional abnormalities from resting state (rs)-fMRI not only in terms of brain activations, but also of whole-brain functional networks and the transitions between maps of activations. The temporal evolution of these networks, assessed with dynamic FC approaches, has recently shown to be relevant in several clinical contexts.

Therefore, the investigators long-term goal is to identify specific resting-state signatures/biomarkers for the individual neuropsychiatric PD symptoms related to disease in dopaminergic OFF-drug state (depression, anxiety, apathy, fatigue, shame, bradyphrenia) and to dopaminergic treatment in dopaminergic ON-drug state (mania, impulse control disorders, hallucinations, psychosis, creative thinking), which might be used in the future as a proxy for the measurement of neuropsychiatric symptoms/fluctuations and thus to assess the effectiveness of specific therapies.

Inclusion Criteria:

• Adults above 18 years old
• Male or female
• Diagnosed with Parkinson's disease
• Able to understand instructions, neuropsychological tests and provide written informed consent
• Able to understand the locally used language of the experimental site and speak fluently
• Presence of neuropsychiatric fluctuations, defined as the sum ≥ 3 of items included in the Ardouin Scale of Behaviour in Parkinson's Disease (ASBPD) part 2

Exclusion Criteria:

• Structural brain disease other than Parkinson's disease
• Substance abuse and/or dependence (other than DRT)
• Ongoing depression with suicidal ideation
• Severe tremors/dyskinesia/ interfering with MRI performance
• Participating in a pharmacological study
• Inability to provide informed consent (legal guardianship)
• MRI contraindications
• Pregnancy