Understanding impulsive behaviour after brain stimulation

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