Feeling-of-knowing in episodic memory: an event-related fMRI study Anat Maril, a, * Jon S. Simons, a,b Jason P. Mitchell, a Bennett L. Schwartz, c and Daniel L. Schacter a a Department of Psychology, Harvard University, Cambridge, MA 02138, USA b Institute of Cognitive Neuroscience, University College London, London, UK c Department of Psychology, Florida International University, Miami, FL, USA Received 8 May 2002; revised 30 October 2002; accepted 21 November 2002 Abstract An individual may fail to recall an item from memory but still feel that it would be recognized on a later test, a retrieval state termed the “feeling-of-knowing” (FOK). In this study we used event-related fMRI and the FOK to examine both encoding- and retrieval-related factors that are associated with different levels of recall performance: successful retrieval of a previously studied item, retrieval failure accompanied by the FOK, and retrieval failure without any FOK. The results revealed one predominant pattern of retrieval-related activation: an intermediate level of activation for FOK—less than that associated with successful recall and greater than that associated with unsuccessful recall (frontal and left parietal cortices). Two further patterns were also observed: greater activation for both successful recall and FOK than for unsuccessful recall (left midlateral prefrontal cortex) and greater activation for successful recall than for both FOK and unsuccessful recall (left MTL). Analysis of encoding trials conditional upon subsequent retrieval success revealed a pattern of activation that appeared to predict subsequent recall, but which further analysis indicated to be a better predictor of subsequent recognition. These results provide evidence that the phenomenology of graded recall is represented neurally in frontal and parietal cortices, but that activation at encoding may not precipitate the different levels of recall experience. © 2003 Elsevier Science (USA). All rights reserved. Episodic memory is typically expressed by successful retrieval of a past experience or by failure to retrieve it. Recent studies using event-related functional magnetic res- onance imaging (fMRI), which allows comparisons be- tween successful and unsuccessful retrieval trials, have re- vealed brain regions associated with success and failure at episodic recognition (Buckner et al., 1998; Henson et al., 1999a, 1999b; Nyberg et al., 2000) and recall of sensory details of previously presented information (Wheeler et al., 2000). Here we report an event-related fMRI study of epi- sodic recall that goes beyond the simple dichotomy between successful and unsuccessful performance. Although neuroimaging studies have focused on the con- trast between successful and unsuccessful performance, ep- isodic retrieval is not always all-or-none. When recognition tests are used to assess memory for studied items, successful recognition can be expressed in two forms: remembering and knowing (Tulving, 1985). Recent studies have exam- ined the neural correlates of recognition accompanied by specific recollection of episodic details (“remember”) ver- sus recognition accompanied by a general sense of famil- iarity (“know”; cf. Eldridge et al., 2000; Henson et al., 1999b). Activity in the prefrontal cortex and MTL regions differentiated between the two forms of recognition. When recall is used to test episodic memory, people sometimes fail to retrieve previously encoded information, but express a feeling-of-knowing (FOK) that they could recognize the information on a later test (Hart, 1965; Nelson and Narens, 1980; Schacter, 1983). In the present study we examined FOK responses, in addition to successful and unsuccessful recall trials, to characterize the brain regions associated with differing levels of episodic recall. We re- cently used event-related fMRI to accomplish a similar objective within the domain of semantic memory. We iden- tified prefrontal cortical regions associated with the “tip-of- * Corresponding author. Department of Psychology, Harvard Univer- sity, William James Hall 882, 33 Kirkland Street, Cambridge, MA 02138. Fax: +1-617-496-3122. E-mail address: amaril@wjh.harvard.edu (A. Maril). R Available online at www.sciencedirect.com NeuroImage 0 (2003) 000 – 000 www.elsevier.com/locate/ynimg 1053-8119/03/$ – see front matter © 2003 Elsevier Science (USA). All rights reserved. doi:10.1016/S1063-8119(03)00014-4 ARTICLE IN PRESS