Examining the Effect of Motivational Context on Response Inhibition: An fMRI Study

Impaired ability to suppress inappropriate behavior (‘response inhibition') is central to Attention-Deficit/Hyperactivity Disorder (ADHD). The neural basis of response inhibition is not fully understood. Using functional magnetic resonance imaging (fMRI), it has been demonstrated that different frontal regions are recruited to guide response inhibition in different contexts. In this study, fMRI was used to investigate the neural basis of response inhibition under the context of increased motivational demands in healthy adults performing two Go/No-go tasks. In both the ‘simple' and ‘motivational' Go/No-go tasks, participants were required to push a button in response to green (‘Go') stimuli but not red (‘No-go') stimuli; however, in the motivational task, there were monetary incentives (correct responses rewarded, incorrect responses punished). We hypothesized that inhibitory activation would be observed in the rostral supplementary motor area (pre-SMA), a region important for selecting motor behavior, for the simple task, and the orbitofrontal cortex (OFC), a region important for making decisions based on motivational information, for the motivational task. Both tasks revealed activation in the pre-SMA; however, no activity was observed in the OFC. This lack of activation may be a result of the motivational task applied in the study not allowing for any change in behavior based on motivation (i.e., they always chose to push on green but not on red, whether or not they were rewarded). Currently, a new version of the motivational task is being piloted to investigate whether the OFC is critical for guiding response inhibition based on motivational information.