Statistical prediction of the future impairs episodic encoding of the present

Brynn E Sherman,Nicholas B Turk-Browne

doi:10.1073/pnas.2013291117

Brynn E Sherman, Nicholas B Turk-Browne

Open Access

https://doi.org/10.1073/pnas.2013291117

Copy DOI

Abstract

Memory is typically thought of as enabling reminiscence about past experiences. However, memory also informs and guides processing of future experiences. These two functions of memory are often at odds: Remembering specific experiences from the past requires storing idiosyncratic properties that define particular moments in space and time, but by definition such properties will not be shared with similar situations in the future and thus may not be applicable to future situations. We discovered that, when faced with this conflict, the brain prioritizes prediction over encoding. Behavioral tests of recognition and source recall showed that items allowing for prediction of what will appear next based on learned regularities were less likely to be encoded into memory. Brain imaging revealed that the hippocampus was responsible for this interference between statistical learning and episodic memory. The more that the hippocampus predicted the category of an upcoming item, the worse the current item was encoded. This competition may serve an adaptive purpose, focusing encoding on experiences for which we do not yet have a predictive model.

Highlights

Memory is typically thought of as enabling reminiscence about past experiences
Episodic memory allows for vivid recollection and nostalgia about past events, whereas statistical learning leads to more generalized knowledge that affords predictions about new situations
When the current experience affords no such expectations, encoding it into memory provides the opportunity to extract new, unknown regularities that enable more accurate predictions in subsequent encounters. After demonstrating this role for statistical learning in episodic memory behaviorally, we identify an underlying mechanism in the brain using functional MRI, based on the recent discovery that both processes depend upon the hippocampus and compete to determine its representations and output [9]

Summary

Introduction

Memory is typically thought of as enabling reminiscence about past experiences. memory informs and guides processing of future experiences. We examine whether the ability to predict what will appear —a signature of statistical learning—reduces encoding of the current experience into episodic memory This hypothesis depends on two theoretical commitments: first, that the adaptive function of memory is to guide future behavior by generating expectations based on prior experience [6] and, second, that memory resources are limited, because of attentional bottlenecks that constrain encoding [7] and/or because new encoding interferes with the storage or retrieval of existing memories [8]. When the current experience affords no such expectations, encoding it into memory provides the opportunity to extract new, unknown regularities that enable more accurate predictions in subsequent encounters After demonstrating this role for statistical learning in episodic memory behaviorally, we identify an underlying mechanism in the brain using functional MRI (fMRI), based on the recent discovery that both processes depend upon the hippocampus and compete to determine its representations and output [9]

Methods

Results

Discussion

Conclusion