Neuropsychologia 48 (2010) 491–497 Contents lists available at ScienceDirect Neuropsychologia journal homepage: www.elsevier.com/locate/neuropsychologia Dissociating the “retrieval success” regions of the brain: Effects of retrieval delay W. Huijbers ∗ , C.M.A. Pennartz, S.M. Daselaar University of Amsterdam, Swammerdam Institute for Life Sciences, Faculty of Science, The Netherlands article info Article history: Received 24 April 2009 Received in revised form 6 October 2009 Accepted 7 October 2009 Available online 14 October 2009 Keywords: Episodic memory fMRI Evidence accumulation Posterior midline region Posterior parietal cortex abstract There is abundant evidence that the hippocampal formation critically supports episodic memory retrieval, the remembering of episodes including contextual details. Yet, a group of other brain regions has also been consistently implicated in successful episodic retrieval. This retrieval success network (RSN) includes the posterior midline region, medial prefrontal cortex (mPFC), and posterior parietal cortex (PPC). Despite these consistent findings, the functional roles of the RSN regions remain poorly understood. Given that vivid remembering leads to high-confidence retrieval decisions, it is unclear whether activity in these regions reflects episodic long-term memory, or is merely associated with retrieval confidence. In order to distinguish between these alternatives, we manipulated study-test delays within the context of a continuous recognition task during fMRI-scanning. The design was based on previous evidence indicating that retrieval at short delays is easier leading to high-evidence mnemonic decisions, whereas retrieval at longer delays is more difficult but also more hippocampus-dependent. Confirming previous findings, we found that retrieval decisions at short delays were more accurate and faster, and that the hippocampus showed greater activity at longer delays. Within the other RSN regions, we found three distinct activation patterns as a function of delay. Similar to the hippocampus, the retrosplenial cortex showed increased activity as a function of retrieval delay. Dorsal PPC and the precuneus showed decreased activity. Finally, the posterior cingulate, medial PFC and ventral PPC showed a V-shaped pattern. These findings support the idea that dorsal PPC and the precuneus are involved in decision-related retrieval processes rather than successful remembering. © 2009 Elsevier Ltd. All rights reserved. 1. Introduction In the past few decades, clinical studies in both animals and humans have yielded overwhelming evidence that the integrity of the hippocampal formation is critical to normal episodic mem- ory retrieval, the remembering of episodes including contextual details (Eichenbaum, Yonelinas, & Ranganath, 2007; Squire, Stark, & Clark, 2004). More recently, functional MRI studies have con- sistently implicated another group of brain regions in successful episodic retrieval. This retrieval success network (RSN) includes the medial prefrontal cortex (mPFC), the posterior parietal cor- tex (PPC), and the posterior midline region (PMR), comprising the precuneus, the posterior cingulate, and the retrosplenial cortex (Buckner, Andrews-Hanna, & Schacter, 2008; Wagner, Shannon, Kahn, & Buckner, 2005). Functional Magnetic Resonance Imag- ing (fMRI) studies of episodic retrieval found greater activity in these regions during correct recognition of studied items, than dur- ∗ Corresponding author. Tel.: +31205257728. E-mail address: w.huijbers@uva.nl (W. Huijbers). ing misses and correctly rejected non-studied items (e.g., Henson, Hornberger, & Rugg, 2005). Moreover, these differences increase with retrieval confidence (e.g., Daselaar, Fleck, & Cabeza, 2006). Yet, despite these consistent findings, the role of the RSN regions in episodic retrieval remains poorly understood. A critical issue is that successful retrieval often leads to high-confidence memory deci- sions. Thus, it is unclear whether activity in the RSN truly reflects episodic long-term memory or is merely associated with confident retrieval decisions. Regarding the latter option, there is substantial evidence that the posterior parietal regions of the RSN are involved in processes supporting perceptual decision-making (Platt & Glimcher, 1999; Shadlen & Newsome, 1996). For instance in the monkey brain, PPC neurons have been linked to the accumulation and integration of evidence from multiple perceptual regions prior to a decision (Shadlen & Newsome, 2001). A functional MRI study on percep- tual recognition has recently reported analogous findings in the human PPC (Ploran et al., 2007). Models of recognition memory also assume that retrieval decisions are based on the accumulation of evidence (Ratcliff, 1978; Ratcliff & Starns, 2009). These models assert that memory judgments are based on a diffusion-like process by which evidence is gathered for or against a memory decision. 0028-3932/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.neuropsychologia.2009.10.006