A neural network model of hippocampal contributions to category learning

Abstract

In addition to its critical role in encoding individual episodes, the hippocampus is capable of extracting regularities across experiences. This ability is central to category learning, and a growing literature indicates that the hippocampus indeed makes important contributions to this form of learning. Using a neural network model that mirrors the anatomy of the hippocampus, we investigated the mechanisms by which the hippocampus may support novel category learning. We simulated three category learning paradigms and evaluated the network’s ability to categorize and recognize specific exemplars in each. We found that the trisynaptic pathway within the hippocampus—connecting entorhinal cortex to dentate gyrus, CA3, and CA1—was critical for remembering exemplar-specific information, reflecting the rapid binding and pattern separation capabilities of this circuit. The monosynaptic pathway from entorhinal cortex to CA1, in contrast, specialized in detecting the regularities that define category structure across exemplars, supported by the use of distributed representations and a relatively slower learning rate. Together, the simulations provide an account of how the hippocampus and its constituent pathways support novel category learning.

Acute stress effects on statistical learning and episodic memory

“…In the absence of stress, there was a negative association between episodic memory (hit rate) and offline statistical learning (pair familiarity). This finding is consistent with the idea that their shared reliance on the hippocampus and output pathways may create interference (Schapiro et al, 2017;Sučević and Schapiro, 2023;Sherman et al, 2023b). However, the relationship between these memory metrics under stress was more nuanced, varying with time since stress and with the predictable nature of the memoranda.…”

“…In line with these ideas, our finding that stress enhances learning processes thought to be dependent on the MSP of the hippocampus in humans raises novel hypotheses about other kinds of learning that may be enhanced by stress. For example, other kinds of integrative learning, such as transitive inference and category learning, have also been associated with the hippocampus (Schlichting et al, 2014(Schlichting et al, , 2017Mack et al, 2016;Schlichting et al, 2021), particularly MSP (Schapiro et al, 2017;Sučević and Schapiro, 2023). This framework may perhaps explain previous behavioral findings that stress can enhance memory for linked episodes (Grob et al, 2023).…”

Evidence for shallow cognitive maps in schizophrenia

“…In future work. our novel approach can be combined with neuroimaging to more directly measure the change in hippocampal representations posited by the shallow cognitive maps hypothesis, and with computational modeling using neural networks to formalize how schizophrenia affects the encoding of structural information (Sučević and Schapiro 2023).…”