The goal of this experimental study with is to understand the underlying mechanisms behind the increase in impulsivity seen in some patients that undergo deep brain stimulation of the subthalamic nucleus for Parkinson's Disease. The main questions it aims to answer are:

What are the distributed network effects of deep brain stimulation to the subthalamic nucleus? How does this correlate with increased impulsivity? Can alternative stimulation settings be used to minimize these?

Participants will complete decision-making tasks whilst their deep brain stimulation devices are turned on and off with simultaneous magnetoencephalography recordings (a type of non-invasive brain scan that measures brain activity in real-time)

Inclusion Criteria:

• Participant is willing and able to give informed consent for participation in the study.
• Male or Female, aged 18 years or above.
• Diagnosed with Parkinson's disease who have required implanted STN electrodes for DBS in addition to their dopamine replacement therapy.
• Diagnosed with or without (control group) impulse control disorders since the diagnosis of Parkinson's Disease.
• Participant willing and able to sit in the MEG scanner and follow instructions.
• Participant willing and able to delay their morning dose of dopamine replacement therapy for up to four hours (180 minutes experimental time + journey time).

Exclusion Criteria:

• Patients with extreme language barrier that cannot understand the purpose or instructions of the study despite the use of an interpreter.
• Other implanted medical devices that may cause artefacts during MEG recordings.
• Participants with a history of co-morbid neurological disorders.
• Participant enrolled onto another clinical trial related to a neurological disorder (including Parkinson's disease) that may interfere with the results of this study.
• Participants who are unable to sit still in a MEG scanner for the duration of this experiment e.g. patients with chronic pain or osteoarthritis. This will be assessed with their primary clinician