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Functional magnetic resonance imaging (fMRI) studies have revealed that activity in the medial temporal lobe (MTL) predicts subsequent memory performance in humans. Because of limited knowledge on cytoarchitecture and axonal projections of the human MTL, precise localization and characterization of the areas that can predict subsequent memory performance are benefited by the use of nonhuman primates in which integrated approach of the MRI- and cytoarchiture-based boundary delineation is available. However, neural correlates of this subsequent memory effect have not yet been identified in monkeys. Here, we used fMRI to examine activity in the MTL during memory encoding of events that monkeys later remembered or forgot. Application of both multivoxel pattern analysis and conventional univariate analysis to high-resolution fMRI data allowed us to identify memory traces within the caudal entorhinal cortex (cERC) and perirhinal cortex (PRC), as well as within the hippocampus proper. Furthermore, activity in the cERC and the hippocampus, which are directly connected, was responsible for encoding the initial items of sequentially presented pictures, which may reflect recollection-like recognition, whereas activity in the PRC was not. These results suggest that two qualitatively distinct encoding processes work in the monkey MTL and that recollection-based memory is formed by the interplay of the hippocampus with the cERC, a focal cortical area anatomically closer to the hippocampus and hierarchically higher than previously believed. These findings will advance the understanding of common memory system between humans and monkeys and accelerate fine electrophysiological characterization of these dissociable memory traces in the monkey MTL.

Original publication

DOI

10.1523/JNEUROSCI.4048-13.2014

Type

Journal article

Journal

J Neurosci

Publication Date

29/01/2014

Volume

34

Pages

1988 - 1997

Keywords

Analysis of Variance, Animals, Association Learning, Brain Mapping, Cues, Female, Functional Laterality, Hippocampus, Image Processing, Computer-Assisted, Macaca fascicularis, Magnetic Resonance Imaging, Male, Mental Recall, Neuropsychological Tests, Oxygen, Pattern Recognition, Visual, Photic Stimulation, Recognition (Psychology), Temporal Lobe, Wakefulness