The anterior-ventrolateral temporal lobe contributes to boosting visual working memory capacity for items carrying semantic information

Rocco Chiou,Matthew A Lambon Ralph

doi:10.1016/j.neuroimage.2017.12.085

Abstract

Working memory (WM) is a buffer that temporarily maintains information, be it visual or auditory, in an active state, caching its contents for online rehearsal or manipulation. How the brain enables long-term semantic knowledge to affect the WM buffer is a theoretically significant issue awaiting further investigation. In the present study, we capitalise on the knowledge about famous individuals as a ‘test-case’ to study how it impinges upon WM capacity for human faces and its neural substrate. Using continuous theta-burst transcranial stimulation combined with a psychophysical task probing WM storage for varying contents, we provide compelling evidence that (1) faces (regardless of familiarity) continued to accrue in the WM buffer with longer encoding time, whereas for meaningless stimuli (colour shades) there was little increment; (2) the rate of WM accrual was significantly more efficient for famous faces, compared to unknown faces; (3) the right anterior-ventrolateral temporal lobe (ATL) causally mediated this superior WM storage for famous faces. Specifically, disrupting the ATL (a region tuned to semantic knowledge including person identity) selectively hinders WM accrual for celebrity faces while leaving the accrual for unfamiliar faces intact. Further, this ‘semantically-accelerated’ storage is impervious to disruption of the right middle frontal gyrus and vertex, supporting the specific and causative contribution of the right ATL. Our finding advances the understanding of the neural architecture of WM, demonstrating that it depends on interaction with long-term semantic knowledge underpinned by the ATL, which causally expands the WM buffer when visual content carries semantic information.

Highlights

Working memory (WM) is a vital cognitive faculty that holds information in a temporary cache
Results showed that WM capacity for objects increased as a function of longer encoding time, which was reflected in significantly greater contralateral delay activity (CDA)
WM capacity for colours remains constant despite more encoding time, which was mirrored in a smaller magnitude of CDA

Summary

Introduction

Working memory (WM) is a vital cognitive faculty that holds information in a temporary cache. In the domain of visual WM, most researchers use abstract stimuli, such as colour patches, in an attempt to gauge the bare capacity while insulating it from the ‘contamination’ of existing knowledge (for review, see Brady et al, 2011). In a recent study, Brady et al (2016) explored how electrophysiological response varies when the WM system is storing objects vs colour patches They looked at the contralateral delay activity (CDA), a neural signature that diminishes in amplitude when information transits from WM to episodic memory. WM capacity for colours remains constant despite more encoding time, which was mirrored in a smaller magnitude of CDA These indicate that, compared to meaningless abstract stimuli, entities that hold ecological relevance (e.g., objects encountered daily in the visual environment) are tackled differently by the WM system, presumably aided by semantic knowledge or familiarity with objects' configuration

Methods

Discussion

Conclusion