Inhibiting Left dlPFC Leaves Relational Evaluative Conditioning Unchanged: Evidence From Electrical Brain Stimulation

Relational evaluative conditioning (EC) paradigms suggest that attitude formation involves both simple co-occurrence-based and relation-based propositional processes. However, the causal role of executive control systems in supporting this propositional learning remains debated. This highly-powered, pre-registered study (N = 76) aimed to causally test the role of the left dorsolateral prefrontal cortex (dlPFC), a key executive control hub, in this process. We replicated (Kukken et al., 2020) relational EC paradigm while applying inhibitory (cathodal) high-definition transcranial direct current stimulation (HD-tDCS) or sham stimulation over the left dlPFC during learning. A Stroop task served as a manipulation check, and Multinomial Processing Tree (MPT) modeling dissociated relational from co-occurrence processes. Results revealed a critical dissociation: while cathodal tDCS successfully impaired performance on the Stroop task, confirming effective neuromodulation, it had no effect on evaluative ratings. Crucially, MPT modeling confirmed that tDCS did not alter the parameters for either relational or co-occurrence processing. These findings challenge the hypothesis that the left dlPFC is indispensable for integrating relational information in EC, suggesting a more nuanced link between domain-general executive control and this fundamental form of attitude formation.