Abstract
Though the ventromedial frontal lobes (VMF) are clearly important for decision-making, the precise causal role of the VMF in the decision process has still not yet fully been established. Previous studies have suggested that individuals with VMF damage violate a hallmark axiom of rational decisions by having intransitive preferences (i.e., preferring A to B, B to C, but C to A), as these individuals are more likely to make cyclical choices (i.e., choosing C over A after previously choosing A over B and B over C). However, these prior studies cannot properly distinguish between two possibilities regarding effects of VMF damage: are individuals with VMF damage prone to choosing irrationally, or are their preferences simply more variable? We had individuals with focal VMF damage, individuals with other frontal damage, and healthy controls make repeated choices across three categories – artwork, chocolate bar brands, and gambles. Using sophisticated tests of transitivity, we find that, without exception, individuals with VMF damage made rational decisions consistent with transitive preferences, even though they more frequently exhibit choice cycles due to a greater variability in their preferences across time. That is, the VMF is necessary for having strong and reliable preferences across time and context, but not for being a rational decision maker. We conclude that VMF damage affects the noisiness with which value is assessed, but not the consistency with which value is sought.
Significance statement The VMF is a part of the brain that is thought to be one of the most important for preference-based choice. Despite this, whether it is needed to make rational choices at all is unknown. Previous studies have not discriminated between different possibilities regarding the critical necessary role that the VMF plays in value-based choice. Our study shows that individuals with VMF damage still make rational decisions consistent with what they prefer, but their choices are more variable and less reliable. That is, the VMF is important for the noisiness with which value is assessed, but not the consistency with which value is sought. This result has widespread implications for rethinking the role of VMF in decision-making.