issociable neural correlates of item and context retrieval in the edial temporal lobes

Although it is generally accepted that the medial temporal lobe (MTL) is critical for episodic memory, the contributions of cortical regions in the MTL, such as the perirhinal (PRc) and parahippocampal (PHc) cortices, remain unresolved. Recent studies have asserted that the PRc supports the processing of object and face information, whereas the PHc supports the processing of scene information. These findings have been used to characterize the PRc and PHc as being important for the memory of objects and scenes, respectively. However, these results are also consistent with the idea that these MTL regions are critical for the memory of stimuli that are processed as either items or contexts. It has been difficult to differentiate between these two accounts given that in most studies, item and context are operationalized as different types of memoranda (e.g., memory for objects compared to memory for background scenes). Here, we tested the extent to which different MTL regions are involved in the retrieval of item or context information when the material type is held constant. Participants encoded pairs of fractal images and edial temporal lobes were oriented to encode one fractal as an item and the other as a context. At test, they were cued with previously studied item or context fractals and asked to retrieve the corresponding associate. Results indicated that on test trials, PRc activity was increased during recall of fractals that were encoded as items, whereas PHc activity was greater during recall of fractals that were encoded as contexts. These results provide direct evidence that, even when stimulus type is held constant, the PRc and PHc are supp preferentially involved in Episodic memory reflects the ability to remember that an object r item was previously presented in a specific temporal or spaial context, such as remembering when or where a person was arlier encountered. Considerable evidence indicates that the hipPlease cite this article in press as: Wang W-C, et al. Dissociable neural co Behav Brain Res (2013), http://dx.doi. org/10.1016/j.bbr. 2013.05. 029 ocampus plays a critical role in episodic memory (for reviews, ee [1,2]). However, controversy persists over the roles of cortical reas (i.e., the perirhinal [PRc] and parahippocampal [PHc] cortices) This study was supported by grants R01 MH083734 and F31 MH096346 from he NIMH. ∗ Corresponding author. Tel. : +1 3109388897; fax: +1 5307522087. E-mail address: wwa@ucdavis.edu (W.-C. Wang). 166-4328/$ – see front matter © 2013 Elsevier B.V. All rights reserved. ttp://dx.doi. org/10.1016/j.bbr. 2013.05. 029 orting memory for item and context information, respectively. © 2013 Elsevier B.V. All rights reserved. in the medial temporal lobes (MTL). Convergent results from studies of tract tracing in animals [3–6] and functional connectivity in humans [7] indicate that the PRc primarily receives higher-order sensory input from several association cortices involved in object identification, whereas the PHc has greater reciprocal connections with the retrosplenial cortex – a region important for spatial memory. Consistent with these findings, there is accumulating evidence to suggest that the relative involvement of these two regions in memory processes may depend on the category of material that is rrelates of item and context retrieval in the medial temporal lobes. to be remembered (for reviews, see [8,9]). That is, the PRc appears to be preferentially engaged in processing object and face information, whereas the PHc appears to be preferentially engaged in processing visual scene information ([10–15]; but see [16,17,54]).