Personality in Parkinson's disease: Clinical, behavioural and cognitive correlates

Affective disorders and personality changes have long been considered pre-motor aspects of Parkinson's disease (PD). Many authors have used the term "premorbid personality" to define distinctive features of PD patients' personality characterized by reduced exploration of new environmental stimuli or potential reward sources ("novelty seeking") and avoidance behaviour ("harm avoidance") present before motor features. The functional correlates underlying the personality changes described in PD, implicate dysfunction of meso-cortico-limbic and striatal circuits. As disease progresses, the imbalance of neurotransmitter systems secondary to degenerative processes, along with dopamine replacement therapy, can produce a reversal of behaviours and an increase in reward seeking, laying the foundations for the emergence of the impulse control disorders. Personality disorders can be interpreted, therefore, as the result of individual susceptibility arising from intrinsic degenerative processes and individual personality features, in combination with extrinsic factors such as lifestyle, PD motor dysfunction and drug treatment. For a better understanding of personality disorders observed in PD and their relationship with the prodromal stage of the disease, prospective clinical studies are needed that correlate different personality profiles with other disease progression markers. Here, we review previous studies investigating the clinical, cognitive and behavioural correlates of personality traits in PD patients.