Graded recall success: an event-related fMRI comparison of tip of the tongue and feeling of knowing.

Insights into memory retrieval processes can be obtained by examining graded recall success, specifically, tip-of-the-tongue (TOT) and feeling-of-knowing (FOK) states. TOT is defined as a recall failure accompanied by a strong feeling of imminent retrieval, and FOK as a recall failure accompanied by a feeling of future ability to recognize the item. The present fMRI study examined the brain regions associated with both intermediate retrieval states in a within-subject, within-memory system design. Subjects were presented with general knowledge questions and were instructed to respond to each with one of four options: Know, indicating successful retrieval of the answer; TOT; FOK; or Don't know, indicating retrieval failure. Different patterns of activation in several brain regions including prefrontal cortex were associated with TOT and FOK states. For example, TOT was associated with activation in anterior cingulate, right dorsal and inferior, and bilateral anterior, prefrontal cortex. TOT and FOK elicited similar levels of activation in parietal regions, both significantly greater than that associated with Know and Don't know responses. The results are interpreted in the light of theories of the role of prefrontal cortex in recall and cognitive conflict.