Modulation of motor cortex activity in a visual working memory task of hand images

Galvez-Pol, Alejandro; Forster, Bettina; Calvo-Merino, Beatriz · 2018 · Crossref

DOI: 10.1016/j.neuropsychologia.2018.05.005

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Summary

This study investigates whether maintaining body-related visual stimuli in working memory (WM) recruits sensorimotor brain regions, extending beyond the visual cortices typically engaged in sensory recruitment models. The authors address the gap in understanding how embodiment frameworks—where perceiving body parts activates one’s own motor representations—apply to the mnemonic consolidation of such stimuli. Specifically, they examine if the neural recruitment during WM maintenance is driven by the sensory modality of the stimulus or by the conceptual nature of the information embedded within it. To isolate motor cortical activity from concurrent visual processing, the researchers employed a novel electroencephalography (EEG) paradigm with 20 participants. Subjects performed a delayed match-to-sample WM task using two stimulus types: images of hands in various postures (body-related) and geometric shapes matching the hand outlines (non-body-related control). The design included two trial types: "visual-only" trials, where participants merely maintained the stimuli, and "visual-motor" trials, where participants executed a task-irrelevant key press during the retention interval. This manipulation elicited motor-cortical potentials (MCPs) alongside visual-evoked potentials. By subtracting the activity from visual-only trials from the compound activity in visual-motor trials, the authors isolated MCPs free from superimposed visual generators. They analyzed the visual contralateral delay activity (vCDA) as an index of visual WM maintenance and the MCPs as an index of motor involvement, manipulating memory load (one vs. two items). Behavioral results showed comparable performance across stimulus types, with accuracy decreasing as memory load increased, confirming that the stimuli were matched in discriminability. Electrophysiologically, the vCDA increased with memory load for both hand and shape stimuli, indicating standard visual WM maintenance. Crucially, the isolated MCPs revealed a distinct pattern: only the maintenance of hand images elicited significant modulation of motor cortical activity based on memory load. The amplitude of the MCPs increased when participants held two hand images compared to one, an effect absent for the geometric shapes. Source localization using s-LORETA confirmed that this differential activity originated in sensorimotor regions. These findings demonstrate that neural recruitment during working memory is not solely determined by the sensory modality of the input but is also driven by the semantic content of the stimulus. The study provides evidence that body-related information engages sensorimotor cortices during the consolidation phase of WM, supporting the embodiment hypothesis. This suggests that the brain utilizes domain-specific processing resources linked to the nature of the perceived information, linking embodiment research with cognitive models of working memory.

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• working memory