Multiple routes to memory: Distinct medial temporal lobe processes build item and source memories

TLDR

Memory enables organisms to distinguish previously encountered from novel stimuli, and while the medial temporal lobe is essential for recognition, the specific roles of its subregions remain debated. The study investigates how activation in distinct medial temporal lobe subregions during encoding predicts subsequent item recognition and source recollection. Event‑related fMRI was employed to measure encoding‑phase activation across hippocampus, perirhinal, and parahippocampal cortex and relate it to later memory performance. Encoding activity in hippocampus and posterior parahippocampal cortex predicted later source recollection but not item recognition, whereas perirhinal cortex activity predicted item recognition but not source recollection, indicating distinct yet complementary learning mechanisms across medial temporal lobe subregions.

Abstract

A central function of memory is to permit an organism to distinguish between stimuli that have been previously encountered and those that are novel. Although the medial temporal lobe (which includes the hippocampus and surrounding perirhinal, parahippocampal, and entorhinal cortices) is known to be crucial for recognition memory, controversy remains regarding how the specific subregions within the medial temporal lobe contribute to recognition. We used event-related functional MRI to examine the relation between activation in distinct medial temporal lobe subregions during memory formation and the ability (i) to later recognize an item as previously encountered (item recognition) and (ii) to later recollect specific contextual details about the prior encounter (source recollection). Encoding activation in hippocampus and in posterior parahippocampal cortex predicted later source recollection, but was uncorrelated with item recognition. In contrast, encoding activation in perirhinal cortex predicted later item recognition, but not subsequent source recollection. These outcomes suggest that the subregions within the medial temporal lobe subserve distinct, but complementary, learning mechanisms.