Control of semantic interference in episodic memory retrieval: fMRI and ERP studies

Episodic memory retrieval critically depends on the ability to use semantic knowledge. Thus, the investigation of memory performance on semantically related items is a powerful means by which interference effects can be evoked. Control of semantic interference involves executive processes such as monitoring and mobilisation of processing resources engaged in episodic memory retrieval (retrieval effort). The present study aimed to investigate neural correlates of semantic interference control processes using event-related functional magnetic resonance imaging (fMRI and event-related potentials (ERP). Subjects studied two word lists assigned to six semantic categories two of which were identical in each list (interference condition). During the test condition subjects performed source judgements on a mixture of both study lists and new words. Behavioural data demonstrated that semantic similarity induced highly reliable semantic interference effects: source attributions of semantically related items resulted in significantly longer reaction times and higher error rates compared to the non-interference condition.The fMRI-study revealed an interference-specific activation pattern in right ventrolateral (VLPFC) and left dorsolateral prefrontal (DLPFC) cortex. We suggest that VLPFC activity reflects neuronal activity associated with both specification of retrieval cues and inhibition of irrelevant information while DLPFC mediates recollection monitoring. ERP analysis showed no significant main effect of interference condition. A median split was used to separate subjects with high and low retrieval effort. Only subjects with large differences in reaction times for the interference condition compared to the control condition showed left frontal ERPs that were more positive-going for the interference condition compared to the non-interference condition. These differences were interpreted as reflecting processes associated with retrieval effort