Unfortunately OAB in adults with PD is difficult to treat. This is largely because the mechanisms underlying OAB in adults with PD are not known. Recent functional MRI (fMRI) studies suggest that certain areas of the brain have an important role in OAB. Blood oxygenation level dependent (BOLD) fMRI is an imaging technique in which neural activity of a region of the brain can be measured by fluctuation in the BOLD signal. It is hoped that the findings of this study will allow the development of new treatments for adults with Parkinson's disease and overactive bladder.