Zero the hero: Evidence for involvement of the ventromedial prefrontal cortex in affective bias for free items

Recent evidence from psycho-economics shows that when the price of an item decreases to theextent that it becomes available for free, one can observe a remarkable increase of subjective utilitytoward this item. This phenomenon, which is not observed for any other price but zero, has beentermed the zero-price effect (ZPE). The ZPE is attributed to an affective heuristic where the positiveaffect elicited by the free status of an item provides a mental shortcut biasing choice towards thatitem. Given that the ZPE relies on affective processing, a key role of the ventromedial prefrontalcortex (vmPFC) has been proposed, yet neuroscientific studies of the ZPE remain scarce. This studyaimed to explore the role of the vmPFC in the ZPE using a novel, within-subject assessment inparticipants with either an acquired (lesion patients) or degenerative (behavioural-variantfrontotemporal dementia patients) lesion of the vmPFC, and age-matched healthy controls. Allparticipants were asked to make a series of choices between pairs of items that varied in price. Onechoice trial involved an equal decrease of both item prices, such that one of the items was pricedzero. In contrast to controls, both vmPFC-lesion and behavioural-variant frontotemporal dementiapatients showed marked reductions in zero-related changes of preference in pairs of gift-cards, butnot for pairs of food items. Our findings suggest that affective evaluations driving the ZPE are alteredin patients with focal or degenerative damage to the vmPFC. This supports the notion of a key role ofthe vmPFC in the ZPE and, more generally, the importance of this region in value-based affectivedecision-making. Our findings also highlight the potential utility of affective heuristic tasks in futureclinical assessments.