Concurrent neuroimaging and neurostimulation reveals a causal role for dlPFC in coding of task-relevant information

The way in which the brain prioritises processing of information relevant for our current goals is widely contested. Many studies implicate the dorsolateral prefrontal cortex (dlPFC), and propose that it drives brain-wide focus by biasing processing in favour of relevant information. An alternative, however, is that dlPFC is involved in the inhibition of irrelevant information. Here, we address this longstanding debate using the inferentially powerful approach of applying transcranial magnetic stimulation during functional magnetic resonance imaging (concurrent TMS-fMRI) and testing for changes in information coding using multivariate pattern analysis (MVPA). We ask whether dlPFC plays a causal role in prioritising information processing, and whether this is through selection of relevant information or inhibition of irrelevant information. Participants attended to one object feature whilst ignoring another feature of the same object. We reasoned that, if dlPFC is necessary for selection, active (disruptive) TMS should decrease coding of attended information compared to the low intensity (control) condition. Conversely, if right dlPFC is crucial for inhibition, active TMS should increase coding of irrelevant information relative to the control condition. The results showed that active TMS decreased coding of relevant information throughout the frontoparietal multiple demand regions, and that this impact was significantly stronger than the effect of TMS on irrelevant information coding, which was not statistically detectable. These data provide causal evidence for a specific role of dlPFC in supporting the representation of task-relevant information and demonstrate the crucial insights into high level cognitive-neural mechanisms possible with the combination of TMS-fMRI and MVPA.