Metabolic state as a modulator of neural event-related potentials for food stimuli in an implicit association test.

The Implicit Association Test (IAT) has become a ubiquitous measure of implicit associations or preferences in several fields of research, including research related to food choices. The neural dynamics of the IAT have been explored in several contexts, but in a food-related IAT with stimuli of natural motivational value they are yet to be studied. Additionally, the effect of metabolic state on them is poorly known. The present study examined the event-related potentials (ERP) in healthy non-obese females (n = 32) while they performed a food-related IAT in two sessions, in a fasted state and after a meal. The results showed differences in the ERP components N400, P3 and LPP by congruence categories. Additionally, the individual N400 and LPP deflections correlated strongly with individual IAT effects. ERP deflections were weaker in the fasted state than after the meal despite greater implicit hedonic motivation towards food in the fasted state. In conclusion, the results suggest that ERPs reflect the IAT effect. The N400, P3 and LPP components were evoked in a food-related IAT in a similar way observed in IAT tests in other contexts, reflecting a difference in meaning and motivation between congruence categories. The strong correlations of individual IAT effect with individual N400 and LPP deflections further suggests that the food-related IAT effect strength reflects the size of implicit food bias seen in neural deflections. Moreover, fasting increased implicit hedonic motivation towards food, but likely reduced cognitive resources at the same time. This could have made it harder to determine the value of novel, task-relevant stimuli, whereas it became easier postprandially and with practice.