Thesis defense Payam Piray (Donders series 249)

1 December 2016

Promotors: prof. I. Toni, prof. R. Cools

Compute to learn. Neural implementation of computations underlying associative learning and decision making

Mental disorders are still a major source of suffering for individuals and their families. In this thesis, we studied brain mechanisms making some individuals impulsive, a psychological trait related to mental disorders, such as addiction. We focused on an important brain area for learning from rewards such as food and money called the striatum and a neuro-chemical primarily released within this area, which is called dopamine. We found that dopamine modulates connectivity between sub-areas of the striatum and the degree of modulation is higher in more impulsive people. We also asked why commonly used dopaminergic medications in Parkinson’s disease make some of the patients pathologically impulsive –so they engage in behavioral addictions such as hypersexuality or binge eating. We found that these medications disrupt learning in impulsive patients, particularly learning from negative consequences of engaging in situations associated with experiencing rewards and punishments. Putting together, our studies suggest that disruptions in brain computations underlying learning predispose individuals to impulsivity and excessive risk taking.