Heavy metals pose detrimental risks to animals (including humans), making them a focus of EU policies. As heavy metals exert neurotoxic effects, the cognitive system might be most susceptible to even low exposure levels, especially when absorption occurs prenatally. A crucial neurocognitive function that may be impaired through heavy metal exposure is response inhibition. Response inhibition allows animals to inhibit inappropriate actions to adapt to ever-changing environments. Failing to inhibit a response may result in (1) fast and risky actions and (2) irrelevant persistence of habits, both of which can have important fitness consequences. Yet, previous work on heavy metals mainly focused on neurochemical and behavioural effects, while ignoring the intermediate neurocognitive level. In this project, I propose to examine how response inhibition mediates the effect of heavy metal exposure and behaviours (i.e. foraging flexibility and mortality through predation) in the wild by using two ecologically valid and uniquely coupled ‘heavy metal – animal’ model systems. First, I will develop a theoretical framework of this mediation. Second, I propose to experimentally test how prenatal heavy metals (i.e. methylmercury and lead) exposure affects response inhibition. Finally, I will quantify to what extent and how heavy metal-induced individual differences in response inhibition are linked to complex behaviours in the wild.