Zero the hero: Evidence for involvement of the ventromedial prefrontal cortex in affective bias for free items
Résumé
Recent evidence from psycho-economics shows that when the price of an item decreases to the
extent that it becomes available for free, one can observe a remarkable increase of subjective utility
toward this item. This phenomenon, which is not observed for any other price but zero, has been
termed the zero-price effect (ZPE). The ZPE is attributed to an affective heuristic where the positive
affect elicited by the free status of an item provides a mental shortcut biasing choice towards that
item. Given that the ZPE relies on affective processing, a key role of the ventromedial prefrontal
cortex (vmPFC) has been proposed, yet neuroscientific studies of the ZPE remain scarce. This study
aimed to explore the role of the vmPFC in the ZPE using a novel, within-subject assessment in
participants with either an acquired (lesion patients) or degenerative (behavioural-variant
frontotemporal dementia patients) lesion of the vmPFC, and age-matched healthy controls. All
participants were asked to make a series of choices between pairs of items that varied in price. One
choice trial involved an equal decrease of both item prices, such that one of the items was priced
zero. In contrast to controls, both vmPFC-lesion and behavioural-variant frontotemporal dementia
patients showed marked reductions in zero-related changes of preference in pairs of gift-cards, but
not for pairs of food items. Our findings suggest that affective evaluations driving the ZPE are altered
in patients with focal or degenerative damage to the vmPFC. This supports the notion of a key role of
the vmPFC in the ZPE and, more generally, the importance of this region in value-based affective
decision-making. Our findings also highlight the potential utility of affective heuristic tasks in future
clinical assessments.