BDNF polymorphism in non-veridical decision making and differential effects of rTMS

Making decisions when an objectively correct option is not obvious, involves different neurobiological mechanisms than "veridical" decision making. The dorsolateral prefrontal cortex (DLPFC) exhibits a distinct pattern of prefrontal activation in non-veridical cognition, but little is known about the role of underlying neurobiological endophenotypes. A functional polymorphism in the brain-derived neurotrophic factor (BDNF) gene, causing a valine (Val) to methionine (Met) amino acid substitution at codon 66, has been shown to be associated with structural and functional changes in DLPFC and affect veridical decision making. We hypothesized that the BDNF genotype may be related to non-veridical cognition. We explored whether the BDNF Val66Met polymorphism affected preferences in a cognitive task devoid of intrinsically correct or false choice, using the Cognitive Bias Task (CBT). We also studied if manipulating the right DLPFC with rTMS stimulation changes non-veridical preferences. Sixteen healthy adults, including 9 Val/Val and 7 Val/Met subjects, participated in the study. Participants with Val/Met genotype expressed a more context-independent, internally driven choice selection preference. Val/Val subjects' selection was more dependent on the context, driven by the properties of external stimuli. rTMS stimulation enhanced a preexisting bias in choice preferences. In Val/Val subjects, TMS stimulation shifted the non-veridical preference bias towards greater dependence on external context, while in Val/Met subjects the CBT score became more context-independent. Our study showed that BDNF genotype is associated with a bias in non-veridical preferences and that Val/Val and Val/Met subjects respond differently to right DLPFC rTMS stimulation, further enhancing their preexisting selection biases.