Approaching the bad and avoiding the good: lateral prefrontal cortical asymmetry distinguishes between action and valence.

Goal pursuit in humans sometimes involves approaching unpleasant and avoiding pleasant stimuli, such as when a dieter chooses to eat vegetables (although he does not like them) instead of doughnuts (which he greatly prefers). Previous neuroscience investigations have established a left-right prefrontal asymmetry between approaching pleasant and avoiding unpleasant stimuli, but these investigations typically do not untangle the roles of action motivation (approach vs. avoidance) and stimulus valence (pleasant vs. unpleasant) in this asymmetry. Additionally, studies on asymmetry have been conducted almost exclusively using electroencephalography and have been difficult to replicate using functional magnetic resonance imaging (fMRI). The present fMRI study uses a novel goal pursuit task that separates action motivation from stimulus valence and a region-of-interest analysis approach to address these limitations. Results suggest that prefrontal asymmetry is associated with action motivation and not with stimulus valence. Specifically, there was increased left (vs. right) activation in dorsolateral prefrontal cortex during approach (vs. avoidance) actions regardless of the stimulus valence, but no such effect was observed for pleasant compared to unpleasant stimuli. This asymmetry effect during approach-avoidance action motivations occurred in the dorsolateral but not orbito-frontal aspects of prefrontal cortex. Also, individual differences in approach-avoidance motivation moderated the effect such that increasing trait approach motivation was associated with greater left-sided asymmetry during approach actions (regardless of the stimulus valence). Together, these results support the notion that prefrontal asymmetry is associated with action motivation regardless of stimulus valence and, as such, might be linked with goal pursuit processes more broadly.