Shared processes resolve competition within and between episodic and semantic memory: Evidence from patients with LIFG lesions

Sara Stampacchia,Hannah E Thompson,Emily Ball,Upasana Nathaniel,Glyn Hallam,Jonathan Smallwood,Matthew A Lambon Ralph,Elizabeth Jefferies

doi:10.1016/j.cortex.2018.07.007

Sara Stampacchia, Hannah E Thompson + Show 6 more

Open Access

https://doi.org/10.1016/j.cortex.2018.07.007

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Abstract

Semantic cognition is supported by two interactive components: semantic representations and mechanisms that regulate retrieval (cf. ‘semantic control’). Neuropsychological studies have revealed a clear dissociation between semantic and episodic memory. This study explores if the same dissociation holds for control processes that act on episodic and semantic memory, or whether both types of long-term memory are supported by the same executive mechanisms. We addressed this question in a case-series of semantic aphasic patients who had difficulty retrieving both verbal and non-verbal conceptual information in an appropriate fashion following infarcts to left inferior frontal gyrus (LIFG). We observed parallel deficits in semantic and episodic memory: (i) the patients' difficulties extended beyond verbal materials to include picture tasks in both domains; (ii) both types of retrieval benefitted from cues designed to reduce the need for internal constraint; (iii) there was little impairment of both semantic and episodic tasks when control demands were minimised; (iv) there were similar effects of distractors across tasks. Episodic retrieval was highly susceptible to false memories elicited by semantically-related distractors, and confidence was inappropriately high in these circumstances. Semantic judgements were also prone to contamination from recent events. These findings demonstrate that patients with deregulated semantic cognition have comparable deficits in episodic retrieval. The results are consistent with a role for LIFG in resolving competition within both episodic and semantic memory, and also in biasing cognition towards task-relevant memory stores when episodic and semantic representations do not promote the same response.

Highlights

Neuropsychological studies provide compelling evidence for the existence of separable episodic and semantic memory stores
We previously found that such multimodal semantic deficits in stroke aphasia reflect difficulties with controlled access to semantic information (Corbett, et al, 2009a; Corbett et al, 2011; Gardner et al, 2012; Noonan et al, 2010; Thompson et al, 2015), and this pattern was reproduced in this sample
Executive/attentional impairment was seen in seven of the ten patients, across four tasks: Elevator Counting with and without distraction from the Test of Everyday Attention (Robertson, Ward, Ridgeway, & Nimmo-Smith, 1994); Ravens Coloured Progressive Matrices (RCPM; Raven, 1962); Brixton Spatial Rule Attainment task (Burgess & Shallice, 1997) and Trail Making Test A & B (Reitan, 1958). This is in line with previous studies which found that deregulated semantic cognition correlated with executive dysfunction in stroke aphasia (Jefferies & Lambon Ralph, 2006; Noonan et al, 2010)

Summary

Introduction

Neuropsychological studies provide compelling evidence for the existence of separable episodic and semantic memory stores. Executive/attentional impairment was seen in seven of the ten patients (see Supplementary Table 4), across four tasks: Elevator Counting with and without distraction from the Test of Everyday Attention (Robertson, Ward, Ridgeway, & Nimmo-Smith, 1994); Ravens Coloured Progressive Matrices (RCPM; Raven, 1962); Brixton Spatial Rule Attainment task (Burgess & Shallice, 1997) and Trail Making Test A & B (Reitan, 1958) This is in line with previous studies which found that deregulated semantic cognition correlated with executive dysfunction in stroke aphasia (Jefferies & Lambon Ralph, 2006; Noonan et al, 2010). The Verbal Paired Associates test from WMS-III was impaired (see below)

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