Dissociation of the Perirhinal Cortex and Hippocampus During Discriminative Learning of Similar Objects

Abstract

Discriminative learning is a paradigm that has been used in animal studies, in which memory of a stimulus is enhanced when it is presented with a similar stimulus rather than with a different one. Human studies have shown that through discriminative learning of similar objects, both item memory and contextual memories are enhanced. However, the underlying neural mechanisms for it are unclear. The hippocampus and perirhinal cortex (PRC) are two possible regions involved in discriminating similar stimuli and forming distinctive memory representations. In this study, 28 participants (15 males) were scanned using high-resolution fMRI when a picture (e.g., a dog) was paired with the same picture, with a similar picture of the same concept (e.g., another dog), or with a picture of a different concept (e.g., a cat). Then, after intervals of 20 min and 1 week, the participants were asked to perform an old/new recognition task, followed by a contextual judgment. The results showed that during encoding, there was stronger activation in the PRC for the "similar" than for the "same" and "different" conditions and it predicted subsequent item memory for the "similar" condition. The hippocampal activation decreased for the "same" versus the "different" condition and the DG/CA3 activation predicted subsequent contextual memory for the "similar" condition. These results suggested that the PRC and hippocampus are functionally dissociated in encoding simultaneously presented objects and predicting subsequent item and contextual memories after discriminative learning.How the brain separates similar input into nonoverlapping representations and forms distinct memory for them is a fundamental question for the neuroscience of memory. By discriminative learning of similar (vs different) objects, both item and contextual memories are enhanced. This study found functional dissociations between perirhinal cortex (PRC) and hippocampus in discriminating pairs of similar and different objects and in predicting subsequent memory of similar objects in their item and contextual aspects. The results provided clear evidence on the neural mechanisms of discriminative learning and highlighted the importance of the PRC and hippocampus in processing different types of object information when the objects were simultaneously presented.

High feature overlap reveals the importance of anterior and medial temporal lobe structures for learning by means of fast mapping

“…This cross-domain role of the PrC suggests that discriminative and mnemonic factors might interact during encoding. In line with this assumption, Chen, Zhou, and Yang (2019) The role of anterior and medial temporal lobe structures in learning by means of fast mapping 6 found that the increased activation of the PrC during the discrimination between two highly similar items at encoding, compared to the discrimination between items from different categories, was predictive of later item recognition memory. Supportive evidence comes from an eye-tracking study by Zhou, Chen, and Yang (2018), who found that more saccades between similar items were also predictive of subsequent item memory.…”

Multiple Exposures Enhance Both Item Memory and Contextual Memory Over Time

“…One for most dissimilar, five for most similar). As one concept triplet had three similar pictures, three similarity rating scores for every two pictures of a triplet were acquired and averaged as one similarity score for each concept (Zhou et al, 2018;Chen et al, 2019). The naming accuracy for the pictures was 0.91 ± 0.12, the familiarity score was 1.81 ± 0.33, and the similarity score was 2.93 ± 0.51.…”

“…All triplets were first randomly assigned to four groups (Groups A-D), with one group used for the "same" condition, one for the "similar" condition, and the other two for the "different" condition (Chen et al, 2019). Next, each group was assigned to three different sets (S1, S2, and S3) for three retention intervals.…”

“…The important feature of discriminative learning is that item memory is enhanced in both detailed and general aspects when two similar objects are compared. After discriminative learning, Chen et al (2019) adopted a recognition test during which participants were presented an old picture or a new but similar picture and thereby requested to make an old/new judgment. The results showed that the hit rate and FA rate were both higher for the "similar" than "different" condition.…”

“…In addition, when participants discriminated similar objects only once, their enhanced item and contextual memories retained until 1 week (Zhou et al, 2018;Chen et al, 2019). But there are intensive debates on whether multiple exposures produce slower forgetting of subsequent memory (e.g., Slamecka and McElree, 1983;Bogartz, 1990;Gardiner and Java, 1991;Hockley and Consoli, 1999;Yang et al, 2016).…”