Stimulating the medial prefrontal cortex disrupts inhibitory control over memory by modulating frontal and parietal brain regions

The act of recalling memories can paradoxically lead to the forgetting of other associated memories, a phenomenon known as retrieval-induced forgetting (RIF). This effect is thought to be mediated by inhibitory control mechanisms in the prefrontal cortex of the brain. Here we investigated whether stimulation of the medial prefrontal cortex (mPFC) with transcranial direct current stimulation modulates inhibitory control during memory retrieval in a RIF paradigm. In a randomized study, fifty participants received either real or sham stimulation, before performing retrieval practice on target memories. After retrieval practice, a final test was administered to measure the impact of stimulation on RIF. We found that stimulation selectively increased the retrieval accuracy of non-target memories and thus decreased RIF, suggesting a disruption of inhibitory control. Meanwhile, no change arose for the retrieval accuracy of target memories. The reduction in RIF was caused by a more pronounced beta desynchronization within the left dorsolateral prefrontal cortex (left-DLPFC), in an early time window (<500 msec) after the onset of the cue during retrieval practice. This, in turn, led to a stronger beta desynchronization within the parietal cortex in a later time window, an established marker for successful memory retrieval. Together, our results establish the causal involvement of the mPFC in actively suppressing competing memories and we demonstrate that while forgetting arises as a consequence of retrieving specific memories, these two processes are functionally independent. Finally, we demonstrate that beta desynchronization in the fronto-parietal brain regions indicates the disruption of inhibitory control.