Familiarity and recollection in the medial temporal lobe.

Editor's Note: These short, critical reviews of recent papers in the Journal, written exclusively by graduate students or postdoctoral fellows, are intended to summarize the important findings of the paper and provide additional insight and commentary. For more information on the format and purpose of the Journal Club, please see Review of Kirwan et al. Everyday experience informs us that there are two ways to recognize a stimulus as having been encountered on a previous occasion. In some cases, we experience a general feeling of memory, or familiarity, which indicates that the presented event has been experienced before. On other occasions, we remember or recollect contextual details from a previous encounter. Both routes, namely familiarity and recollection, lead to recognition, but the way they operate is a matter of great dispute in the field of cognitive neuroscience (Parks and Yonelinas, 2007; Squire et al., 2007). Despite agreement that at the functional level, recognition draws on familiarity and recollection, there is minimal consensus regarding the participation of medial temporal lobe (MTL) structures in supporting these two components. According to one view, different MTL structures, albeit highly interconnected, are responsible for accomplishing distinct computations during recognition. Familiarity has been reported to rely on the perirhinal cortex, whereas recollection is thought to be mediated by the hippocampus (Yonelinas et al., 2002; Ranganath et al., 2004). Functional magnetic resonance imaging (fMRI) studies using a scanned encoding phase and a subsequent memory test [i.e., subsequent memory effect paradigm; Paller and Wagner (2002)], have shown differential activations within the MTL. The hippocampus has shown a greater response to later recollected events, whereas the perirhinal cortex appears more important for encoding later familiar stimuli. It also responds more to variations in item memory strength (Ranganath et al., 2004). Other researchers, however, regard familiarity and recollection as products of a single underlying variable characterized by varying degrees of strength. On this scale, familiarity reflects the lower memory strength and recollection the higher (Squire et al., 2007). According to this view, all MTL structures contribute equally to familiarity and recollection. For example, Shrager et al. (2008) have shown that activity in the MTL (including both the hippocampus and the perirhinal cortex) during encoding of words predicts the strength of later memory. In this study, a subsequent recognition test using a confidence rating (1– 6) for general memory feeling was used, without discriminating between familiar and recollected events. Many controversies …