Serotonergic modulation of meta-control parameters: Temporal discounting rate, probabilistic discounting rate, learning rate, and habitisation (completed)

Serotonin (5 HT) plays a key role in a wide variety of emotional, cognitive and behavioural processes and thereby modulates volitional control. Based on a computational framework we assume that tonic 5 HT levels (together with tonic dopamine levels) code the overall average outcome, which represents a sort of baseline, and that via this mechanism 5 HT modulates the balance between complementary control processes. Within this framework, increasing the overall average outcome, e.g. by depleting 5 HT, should on the one hand increase opportunity costs of time. Thus waiting for rewards or deliberation to obtain them becomes more costly, and consequently cognitive control should be biased towards steeper temporal discounting of rewards as well as a tendency towards fast and habitual responding. On the other hand, an increased overall baseline decreases the weight of rewards, but increases that of punishments. Therefore, 5 HT should affect risk seeking to obtain rewards or to avoid punishments, and also differently affect learning rates from either rewards or punishments. Specifically, we aim to understand the behavioural and neural mechanisms by which 5 HT modulates complementary meta-control parameters. To investigate this, participants will perform a set of tasks designed to assess meta-control parameters such as the temporal discounting rate, probabilistic discounting rate, learning rate and the balance between habitual and goal-directed behaviour during functional magnetic resonance imaging (fMRI) and additionally undergo pharmacological manipulations of tonic 5 HT levels.