Parkinson's disease is a progressive neurodegenerative disorder characterised by the loss of dopaminergic neurons in the basal ganglia and the thalamo-cortical circuitry, leading to alterations in motor control. In addition, there is a growing body of evidence that suggests that the basal ganglia also underlie higher-level functions such as cognition, emotion and motivation.

A group of researchers coordinated by Salvatore Maria Aglioti, and involving Sapienza University of Rome, Istituto Italiano di Tecnologia, Fondazione Santa Lucia IRCCS, published a literature review aimed at investigating moral cognition, and in particular moral decision-making processes, such as lying or telling the truth, in patients who have Parkinson's disease.

The analysis of the scientific literature revealed the presence of two different behavioural tendencies: hyper-honesty, i.e. a lower propensity to lie compared to the control groups, even when the lie involved an economic gain, and hypo-honesty, i.e. a higher propensity to lie compared to the control groups. In particular, the tendency to lie was often associated with the additional diagnoses of impulse control disorder and dopamine dysregulation syndrome.

Patients who have impulse control disorder in addition to Parkinson's disease," explains Giorgia Ponsi, a psychologist and the study's first author, "show a reduced amount of the dopamine transporter in the dorsal striatum, which is the region of the brain involved in the motor and cognitive aspects of decision-making. This is associated with an increased presynaptic release of dopamine in the ventral striatum, the brain region that is part of the reward circuitry and is involved in the motivational aspects of decision-making in response to external rewards. This implies that, for example, the prospect of winning money has a higher motivational value for a person with Parkinson's disease and impulse control disorder."

"The study of these behaviours in people with Parkinson's disease makes it possible to understand, through neuroscience, the complex chain of events that guide us in our daily choices," said Salvatore Maria Aglioti. "The ultimate goal is to be able to identify therapeutic strategies that, through the use of drugs or neurorehabilitation, can help restore the balance interrupted by the disease."

According to the authors of the study, the main hypothesis derived from this analysis is that dysfunctions in the motivational system, in particular dopaminergic imbalance between the dorsal and ventral striatum, may increase or decrease the salience of external rewards (e.g. money or food) and thus explain both behavioural tendencies (hyper- and hypo-honesty) reported in the literature.

References:

Ponsi, G., Scattolin, M., Villa, R., Aglioti, S. M. Human moral decision-making through the lens of Parkinson’s disease. npj Parkinsons Dis. 7, 18 (2021). https://doi.org/10.1038/s41531-021-00167-w

Further Information

Salvatore Maria Aglioti
Department of Psychology
salvatoremaria.aglioti@uniroma1.it