Association between striatal volumes and clinical measures. Each circle represents one Parkinson’s disease patient, either with normal cognition (PDN), mild cognitive impairment (PD-MCI), or dementia (PDD). Left column: The volume of each striatal structure was positively associated with overall cognitive status, as assessed by the Montreal Cognitive Assessment (MoCA, maximum score = 30). Middle column: Both structures decreased in volume with increasing motor disease severity, as measured by the Hoehn & Yahr scale. Right column: The volume of both structures decreased with age. The striatal associations with both MoCA and Hoehn & Yahr did not survive correction for age. The clear collinearity of the predictors, however, (i.e., older patients were more likely to be cognitively impaired and to have worse motor impairment) makes the attribution of causality difficult. Striatal volumes are expressed as percentage of intracranial volume (%ICV).