Neural correlates of episodic retrieval: an fMRI study of the part-list cueing effect

Episodic retrieval is supported by multiple forms of cognitive control that depend on prefrontal cortex. However, within prefrontal cortex, the regional specificity for different control processes is still largely underspecified. Here we used fMRI to investigate the processes involved in part-list cueing, a phenomenon entailing the reduction of memory performance when some of the "to-be-remembered items" are presented during retrieval. Retrieval inhibition and strategy disruption have been proposed as possible underlying causes of this surprising effect. Critically, different encoding conditions can dissociate these two hypotheses, as this is thought to have a different impact on strategy-related versus inhibition-related processes. Accordingly, we compared part-list versus no part-list retrieval conditions, following high versus low associative encoding conditions. This revealed activation of the left frontopolar and right dorsolateral prefrontal cortex in conditions of part-list cueing retrieval, but only following low associative encoding. These results are consistent with the inhibitory or interference resolution accounts of part-list cueing, suggesting a critical role of between-items competition and high monitoring demands at retrieval. In addition, we also examined brain activation during the encoding phase, specifying further possible anatomo-functional links between encoding and retrieval processes. The results suggest that different encoding conditions induce distinct patterns of activation at retrieval, corroborating the idea that they promote the adoption of different retrieval strategies. The implications of the results are discussed in relation to the cognitive mechanisms of inhibition, interference resolution, and encoding/retrieval strategies for episodic memory.