Role of the inferior frontal gyrus and impulsivity in approach motivation: A low-frequency repetitive transcranial magnetic stimulation study.

Human actions are motivated by drives to approach positive outcomes or avoid adverse outcomes. Neurophysiological studies have associated the right-lateralized inferior frontal gyrus (IFG) with the regulation of approach motivation and individual differences in impulsivity, particularly in relation to deficits in motivational regulation. These studies suggest that the right IFG may inhibit approach-motivational tendencies. The current study investigated the causal role of the right IFG in motivational regulation and whether individual differences in impulsivity interact with the IFG to predict motivational regulation. The current study (N = 33) employed low-frequency repetitive transcranial magnetic stimulation to transiently inhibit the functioning of the right or left IFG before a mobile approach-avoidance task. Results revealed that inhibition of the right, but not the left, IFG causes greater approach-motivated behavior in individuals high in impulsivity. These results suggest that the right IFG acts as an inhibitory mechanism that plays a causal role in approach motivation when a "motivational amplifier" is present, such as greater trait impulsivity. This study also suggests that the right IFG is especially important for regulating motivation in individuals with deficits in inhibitory control. These findings inform models of impulsivity and personality by revealing the causal role of the right IFG as a neural substrate of motivational inhibition and by demonstrating how individual differences in impulsivity can impact motivational regulation.