Advancing working memory research through cortico-cortical transcranial magnetic stimulation

Abstract

The neural underpinnings of working memory (WM) have been of continuous scientific interest for decades. As the understanding of WM progresses and new theories, such as the distributed view of WM, develop, the need to advance the methods used to study WM also arises. This perspective discusses how building from the state-of-the-art in the field of transcranial magnetic stimulation (TMS), and utilising cortico-cortical TMS, may pave the way for testing some of the predictions proposed by the distributed WM view. Further, after briefly discussing current barriers that need to be overcome for implementing cortico-cortical TMS for WM research, examples of how cortico-cortical TMS may be employed in the context of WM research are provided, guided by the ongoing debate on the sensory recruitment framework.

Keywords: ccPAS; cortico-cortical; paired associative stimulation; sensory recruitment; transcranial magnetic stimulation; working memory.

Figure 1

(A) Example dual-coil design of cortico-cortical transcranial magnetic stimulation targeting occipitoparietal networks. One coil targets occipital regions (blue) and another targets parietal regions (red). (B) Examples of stimulation protocols, with a weaker (subthreshold intensity) pulse in one region preceding a stronger (threshold intensity) pulse in another region. Based on the principles of spike-timing dependent plasticity, interconnected networks can be strengthened when the initial, weaker, pulse targets a lower-level region, followed by a stronger pulse in a higher-level region (top), or weakened when the initial pulse targets the higher-level region, followed by the lower-level region (bottom).

Figure 2

Examples of potential cortico-cortical transcranial magnetic stimulation (TMS) study designs to investigate the debated sensory recruitment framework. (A) Pre-/post- design where cortico-cortical paired associative stimulation is applied between blocks of working memory task trials. (B) Experimental design where different conditions of cortico-cortical TMS are applied during the delay of each working memory task trial.