Pupil size reflects successful encoding and recall of memory in humans

Michal T Kucewicz,Jaromir Dolezal,Brent M Berry,Vaclav Kremen,Gregory A Worrell,Vratislav Fabian,Laura R Miller,Abigail L Magee

doi:10.1038/s41598-018-23197-6

Abstract

Pupil responses are known to indicate brain processes involved in perception, attention and decision-making. They can provide an accessible biomarker of human memory performance and cognitive states in general. Here we investigated changes in the pupil size during encoding and recall of word lists. Consistent patterns in the pupil response were found across and within distinct phases of the free recall task. The pupil was most constricted in the initial fixation phase and was gradually more dilated through the subsequent encoding, distractor and recall phases of the task, as the word items were maintained in memory. Within the final recall phase, retrieving memory for individual words was associated with pupil dilation in absence of visual stimulation. Words that were successfully recalled showed significant differences in pupil response during their encoding compared to those that were forgotten – the pupil was more constricted before and more dilated after the onset of word presentation. Our results suggest pupil size as a potential biomarker for probing and modulation of memory processing.

Highlights

Pupil responses are known to indicate brain processes involved in perception, attention and decisionmaking
These estimates were normalized for every subject within each encoding-recall procedure of a given word list and averaged in 12 s bins centered in the middle of each phase, showing a trend of increasing pupil size with the successive phases of the task (Fig. 1b)
Our results show that the signal sampled from tracking changes in pupil area contains information about the brain states and cognitive processes underlying memory encoding, maintenance and recall

Summary

Introduction

Pupil responses are known to indicate brain processes involved in perception, attention and decisionmaking. They can provide an accessible biomarker of human memory performance and cognitive states in general. More recent studies have shown that high-resolution tracking of pupil size can be used to predict perception of specific stimuli[4] and even the voluntary decisions about attending the stimuli[5]. In these experiments, pupil size alone was able to predict an overt decision about timing an action and a covert decision about choice of the stimulus[5], suggesting a link between pupil responses and the higher-order brain systems supporting cognition, decision-making and/or execution of actions. Pupillometry was proposed to provide a signal for ‘strength of memory’13, ‘memory retrieval’[15], and ‘neural novelty’[14]

Methods

Results

Conclusion