Download files
Abstract
Patients with advanced Parkinson’s Disease (PD) commonly suffer with significant executive dysfunction and concomitant visual hallucinations. Although the underlying pathophysiology remains poorly understood, numerous studies have highlighted the strong association between these neuropsychiatric features suggesting that they may share common neural pathways. Whilst previous neuroimaging studies have identified widespread volume loss across a number of cortical regions, to date no studies have utilised Proton Magnetic Resonance Spectroscopy (MRS) to provide insights into how neurometabolic changes may relate to such symptoms. In this study, twenty patients underwent MRS to determine the N-Acetyl Aspartate/Creatine ratio, which reflects the degree of neuronal integrity in neurodegenerative diseases. Voxels were obtained from a test region within the anterior cingulate cortex, an area critical for a wide range of executive mechanisms as well as from a control volume in the posterior cingulate cortex. Lower N-Acetyl Aspartate/Creatine ratios in the anterior but not the posterior cingulate cortex significantly correlated with poorer executive function on tasks of attentional set-shifting and response inhibition. In addition, lower levels of this metabolite were associated with more severe psychotic symptoms (as measured by the Scales for Outcomes in Parkinson's disease-Psychiatric Complications) and poorer performance on the bistable percept paradigm, a recently developed neuropsychological probe of visual hallucinations in PD. Levels of N-Acetyl Aspartate/Creatine were significantly lower in hallucinators compared to non-hallucinators within the anterior cingulate cortex but did not differ in the posterior cingulate cortex. These results suggest that loss of neuronal integrity within the anterior cingulate cortex plays an important role in the pathophysiology underlying executive functioning and visual hallucinations in PD.