TDCS over the right inferior frontal gyrus disrupts control of interference in memory: A retrieval-induced forgetting study

- Retrieval-Induced Forgetting was employed as an index of memory control efficiency.
- Human participants received either sham or real tDCS during the memory control task.
- Across two experiments, real stimulation impaired memory control performance.
- Observed tDCS effects varied widely across different categories of stimuli.
- No effects of stimulation emerged in an ancillary measure of motor stopping ability.

Retrieving information from episodic memory may result in later inaccessibility of related but task-irrelevant information. This phenomenon, known as retrieval-induced forgetting, is thought to represent a specific instance of broader cognitive control mechanisms, that would come into play during memory retrieval, whenever non-target competing memories interfere with recall of target items. Recent neuroimaging studies have shown an association between these mechanisms and the activity of the right Prefrontal Cortex. However, so far, few studies have attempted at establishing a causal relationship between this brain region and behavioural measures of cognitive control over memory. To address this missing link, we delivered transcranial Direct Current Stimulation (tDCS) over the right Inferior Frontal Gyrus (rIFG) during a standard retrieval-practice paradigm with category-exemplar word pairs. Across two experiments, tDCS abolished retrieval-induced forgetting to different degrees, compared to the sham control group whereas no effects of stimulation emerged in an ancillary measure of motor stopping ability. Moreover, influence analyses on specific subsets of the experimental material revealed diverging patterns of results, which depended upon the different categories employed in the retrieval-practice paradigm. Overall, the results support the view that rIFG has a causal role in the control of interference in memory retrieval and highlight the often underestimated role of stimulus material in affecting the effects. The present findings are therefore relevant in enriching our knowledge about memory functions from both a theoretical and methodological perspective.