Characterizing common and dissociable involvement of medial temporal lobe regions during episodic source memory retrieval and analogical reasoning

Westphal, A.J., Reggente, N., Ito, K., Fortuna, W.H., Nawabi, Y., Milstein, M., & Rissman, J.


 SfN 2013 Abstract

Episodic memory and analogical reasoning tasks tend to engage many common frontoparietal structures, perhaps owing to their common demands for declarative memory retrieval and relational integration. Regions of the medial temporal lobe (MTL), well known to play a critical role in the encoding and retrieval of episodic memories, have also been shown to contribute to relational reasoning. We aimed to expand upon these findings by performing a direct comparison of memory- and reasoning-related MTL activity profiles and assessing how these regions communicate with distinct cortical networks to support different task demands. We examined fMRI activity and functional connectivity (FC) of the hippocampus (HIP), parahippocampal cortex (PHC), and perirhinal cortex (PRC) in a novel experimental paradigm featuring closely matched memory and reasoning tasks, both requiring judgments on 4-word stimulus arrays. One day prior to fMRI scanning, subjects (N = 20) encoded 80 words under two different mental imagery conditions. During the scanned memory task, subjects were to identify the word they previously studied and specify the encoding context, if possible. During the analogical reasoning task, subjects were to assess if the top and bottom word pairs shared the same semantic relationship or else indicate the number of non-analogous semantic relationships. Univariate parameter estimates extracted from HIP, PHC, and PRC all showed greater activity for source retrieval versus item familiarity. Activity in the PRC was significantly greater for correct versus incorrect source judgments; this effect also trended in HIP and PHC. During the reasoning task, HIP and PHC showed significantly greater activation on trials with valid analogies than on trials with no semantic relationships, whereas PRC activated strongly during all reasoning task conditions where semantic relationships were present. Task-dependent FC contrasting reasoning and memory was analyzed using psychophysiological interactions analysis. Left HIP demonstrated preferential coupling with both default mode and cognitive control network (CCN) structures for memory and bilateral MTL and lateral temporal regions for reasoning. Left PHC showed preferential coupling with CCN structures for memory and the supramarginal gyrus for reasoning. Left PRC demonstrated stronger coupling with precuneus for memory and occipital structures for reasoning. Taken together, these results confirm prior findings of MTL involvement in episodic source retrieval, while also documenting putative MTL contributions to analogical reasoning and distinct profiles of cortical network coupling across task sets.

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