Investigating the Functional Utility of the Left Parietal ERP Old/New Effect: Brain Activity Predicts within But Not between Participant Variance in Episodic Recollection.

Catherine A Macleod,David I Donaldson

doi:10.3389/fnhum.2017.00580

Catherine A Macleod, David I Donaldson

Open Access

https://doi.org/10.3389/fnhum.2017.00580

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Abstract

A success story within neuroimaging has been the discovery of distinct neural correlates of episodic retrieval, providing insight into the processes that support memory for past life events. Here we focus on one commonly reported neural correlate, the left parietal old/new effect, a positive going modulation seen in event-related potential (ERP) data that is widely considered to index episodic recollection. Substantial evidence links changes in the size of the left parietal effect to changes in remembering, but the precise functional utility of the effect remains unclear. Here, using forced choice recognition of verbal stimuli, we present a novel population level test of the hypothesis that the magnitude of the left parietal effect correlates with memory performance. We recorded ERPs during old/new recognition, source accuracy and Remember/Know/Guess tasks in two large samples of healthy young adults, and successfully replicated existing within participant modulations of the magnitude of the left parietal effect with recollection. Critically, however, both datasets also show that across participants the magnitude of the left parietal effect does not correlate with behavioral measures of memory – including both subjective and objective estimates of recollection. We conclude that in these tasks, and across this healthy young adult population, the generators of the left parietal ERP effect do not index performance as expected. Taken together, these novel findings provide important constraints on the functional interpretation of the left parietal effect, suggesting that between group differences in the magnitude of old/new effects cannot always safely be used to infer differences in recollection.

Highlights

Since the 1980’s (Johnson, 1995) event-related potential (ERP) studies of episodic memory have routinely revealed parietal ‘retrieval success’ effects – neural activity associated with remembering events from the past
The results presented here indicate that the empirically derived relationships are more complex, with significant relationships found within tasks, withinmeasures, but not between measures
Within participants, the magnitude of the left parietal effect increased in conditions associated with recollection – larger old/new effects were seen for R than K, and Source Correct than Source Incorrect ERPs

Summary

Introduction

Since the 1980’s (Johnson, 1995) event-related potential (ERP) studies of episodic memory have routinely revealed parietal ‘retrieval success’ effects – neural activity associated with remembering events from the past. The left parietal effect has been shown to modulate with the Remember/Know (R/K) procedure (Smith, 1993; Düzel et al, 1997), depth of processing (Rugg et al, 1998), amount of information recollected (Vilberg et al, 2006; Vilberg and Rugg, 2009), accuracy and number of source judgments made (Wilding and Rugg, 1996; Trott et al, 1997), retrieval of associative information (Donaldson and Rugg, 1998), and number of repeated study-test blocks (Johnson et al, 1998). A seminal example is provided by Rugg et al (1998), who used a within participant design to compare old/new effects elicited by retrieval of words that had originally received deep or shallow processing at study In this case, participants exhibited better performance, and larger left parietal old/new effects, following deep (semantic) than shallow (perceptual) encoding. The accumulated ERP data strongly suggests that increases in recollection lead to increases in left parietal old/new effect magnitude

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