Right hemisphere occipital rTMS impairs working memory in visualizers but not in verbalizers

Sven Hilbert,Stephan Goerigk,Michaela Mcassey,Patrick Schwaferts,Monika Gruber,Paul Christopher John Taylor,Markus Bühner

doi:10.1038/s41598-019-42733-6

Abstract

Distinguishing between verbal and visual working memory processes is complicated by the fact that the strategy used is hard to control or even assess. Many stimuli used in working memory tasks can be processed via verbal or visual coding, such as the digits in the digit span backwards task (DSB). The present study used repetitive transcranial magnetic stimulation (rTMS) to examine the use of visual processing strategies in the DSB. A total of 47 German university students took part in the study, 23 spontaneously using a verbal processing strategy and 24 using a visual strategy. After rTMS to the right occipital cortex, visualizers showed a significantly stronger mean performance decrease compared to verbalizers. The results indicate that the visual cortex is more critical for visualizers compared to verbalizers in the DSB task. Furthermore, the favored processing modality seems to be determined by the preference for a cognitive strategy rather than the presentation modality, and people are aware of the applied strategy. These findings provide insight into inter-individual differences in working memory processing and yield important implications for laboratory studies as well as clinical practice: the stimulus does not necessarily determine the processing and the participant can be aware of that.

Highlights

Working memory (WM) processes describe a cognitive system responsible for temporary storage and manipulation of information
It was found that participants using a visual strategy performed significantly worse after occipital stimulation compared to the control condition, while verbalizers showed no significant decrease. It indicated that (i) inter-individual differences exist in the processing of optically presented digits, that (ii) participants are aware of their strategies leading to these differences, and that (iii) a visual processing strategy is more dependent on occipital cortex functioning than a verbal processing strategy
The findings extend Hilbert et al.’s17 results, which indicated that different cognitive strategies lead to performance differences in a dual task requiring verbal as well as visual processing, indicating different cortical processing associated with verbal versus visual strategies in the digit span backwards” task (DSB)

Summary

Introduction

Working memory (WM) processes describe a cognitive system responsible for temporary storage and manipulation of information. Preceding most state-based conceptions of working memory, Baddeley & Hitch[9] proposed one of the last century’s most significant models It includes a master system, the central executive, and two slave systems, termed “visuospatial sketchpad” and “phonological loop”, which are thought to be involved in verbal and visual working memory tasks, respectively. Verbal and visual processing strategies have been identified as the two most prominent approaches for cognitive tasks[15] and people favoring one of the strategies can be divided into groups characterized by their typical processing[16]: verbalizers typically use articulatory techniques (i.e., inner rehearsal), while visualizers tend to adopt mental imagery These strategies, naturally, go hand in hand with the visual and the verbal working memory subsystems outlined in Baddeley and Hitch’s model. The left temporo-parietal areas[31,32] have been targeted via TMS to affect verbal working memory performance, while parietal stimulation can alter visual working memory performance[33]

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Conclusion