Incidental Memory Encoding Assessed with Signal Detection Theory and Functional Magnetic Resonance Imaging (fMRI).

Benjamin Clemens,Ute Habel,Nina Romanczuk-Seiferth,Kathrin Koch,Katharina Pauly,N Jon Shah,Volker Backes,Thilo Kellermann,Frank Schneider,Christina Regenbogen

doi:10.3389/fnbeh.2015.00305

Abstract

In functional magnetic resonance imaging (fMRI) studies that apply a “subsequent memory” approach, successful encoding is indicated by increased fMRI activity during the encoding phase for hits vs. misses, in areas underlying memory encoding such as the hippocampal formation. Signal-detection theory (SDT) can be used to analyze memory-related fMRI activity as a function of the participant’s memory trace strength (d′). The goal of the present study was to use SDT to examine the relationship between fMRI activity during incidental encoding and participants’ recognition performance. To implement a new approach, post-experimental group assignment into High- or Low Performers (HP or LP) was based on 29 healthy participants’ recognition performance, assessed with SDT. The analyses focused on the interaction between the factors group (HP vs. LP) and recognition performance (hits vs. misses). A whole-brain analysis revealed increased activation for HP vs. LP during incidental encoding for remembered vs. forgotten items (hits > misses) in the insula/temporo-parietal junction (TPJ) and the fusiform gyrus (FFG). Parameter estimates in these regions exhibited a significant positive correlation with d′. As these brain regions are highly relevant for salience detection (insula), stimulus-driven attention (TPJ), and content-specific processing of mnemonic stimuli (FFG), we suggest that HPs’ elevated memory performance was associated with enhanced attentional and content-specific sensory processing during the encoding phase. We provide first correlative evidence that encoding-related activity in content-specific sensory areas and content-independent attention and salience detection areas influences memory performance in a task with incidental encoding of facial stimuli. Based on our findings, we discuss whether the aforementioned group differences in brain activity during incidental encoding might constitute the basis of general differences in memory performance between HP and LP.

Highlights

Human beings encounter a plethora of everyday events, subjective experiences, and affective states, not all of these are transformed into permanent memories
We demonstrated that post-experimental group assignment and memory performance itself was significantly associated with functional magnetic resonance imaging (fMRI) activity during successful incidental encoding in the insula/temporo-parietal junction (TPJ) and in the fusiform gyrus (FFG), with an advantageous processing of remembered compared to forgotten items in the high performers (HP) compared to the low performers (LP) group
Signal-detection theory (SDT)-derived measures of behavioral recognition performance correlated with brain activity during incidental encoding in regions that are specialized for detection of salient stimuli, stimulus-driven attention (TPJ), and content-specific processing of mnemonic stimuli (FFG)

Summary

Introduction

Human beings encounter a plethora of everyday events, subjective experiences, and affective states, not all of these are transformed into permanent memories. In order to compare events that will later be remembered to those that will be forgotten, a widely used experimental design was developed in the context of event-related functional magnetic resonance imaging (fMRI) It employs an encoding phase, during which stimuli such as words or pictures are presented, and a recognition phase, or subsequent memory test, during which participants have to indicate which stimuli have already been presented in the encoding phase and which ones are new. Whereas increased BOLD activations most likely relate to the actual implementation and performance of various mnemonic operations, deactivations may represent a more general downregulation of the DMN: as a prerequisite for successful memory encoding, the areas comprising the DMN must be deactivated, in order to enable sustained cognitive effort, task performance and the formation of mnemonic representations (Miller et al, 2008; Anticevic et al, 2010)

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