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. 2020 Feb 4;10(2):83.
doi: 10.3390/brainsci10020083.

Combining HF rTMS over the Left DLPFC with Concurrent Cognitive Activity for the Offline Modulation of Working Memory in Healthy Volunteers: A Proof-of-Concept Study

Ilya Bakulin  1 , Alfiia Zabirova  1 , Dmitry Lagoda  1 , Alexandra Poydasheva  1 , Anastasiia Cherkasova  1 , Nikolay Pavlov  1 , Peter Kopnin  1 , Dmitry Sinitsyn  1 , Elena Kremneva  1 , Maxim Fedorov  2 , Elena Gnedovskaya  1   2 , Natalia Suponeva  1 , Michael Piradov  1
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Free PMC article

Combining HF rTMS over the Left DLPFC with Concurrent Cognitive Activity for the Offline Modulation of Working Memory in Healthy Volunteers: A Proof-of-Concept Study

Ilya Bakulin et al. Brain Sci. .
Free PMC article

Abstract

It has been proposed that the effectiveness of non-invasive brain stimulation (NIBS) as a cognitive enhancement technique may be enhanced by combining the stimulation with concurrent cognitive activity. However, the benefits of such a combination in comparison to protocols without ongoing cognitive activity have not yet been studied. In the present study, we investigate the effects of fMRI-guided high-frequency repetitive transcranial magnetic stimulation (HF rTMS) over the left dorsolateral prefrontal cortex (DLPFC) on working memory (WM) in healthy volunteers, using an n-back task with spatial and verbal stimuli and a spatial span task. In two combined protocols (TMS + WM + (maintenance) and TMS + WM + (rest)) trains of stimuli were applied in the maintenance and rest periods of the modified Sternberg task, respectively. We compared them to HF rTMS without a cognitive load (TMS + WM-) and control stimulation (TMS - WM + (maintenance)). No serious adverse effects appeared in this study. Among all protocols, significant effects on WM were shown only for the TMS + WM- with oppositely directed influences of this protocol on storage and manipulation in spatial WM. Moreover, there was a significant difference between the effects of TMS + WM- and TMS + WM + (maintenance), suggesting that simultaneous cognitive activity does not necessarily lead to an increase in TMS effects.

Keywords: N-back task; cognitive enhancement; cognitive function; cognitive training; dorsolateral prefrontal cortex; neuromodulation; non-invasive brain stimulation; transcranial magnetic stimulation; working memory.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
fMRI paradigm with the modified Sternberg task used for individualized determination of stimulation target.
Figure 2
Figure 2
Illustration of high-frequency repetitive transcranial magnetic stimulation (HF rTMS) protocols used in the study. ITI, intertrain interval, TMS + WM + (maintenance), HF rTMS over the left DLPFC during maintenance period of the Sternberg task; TMS + WM + (rest), HF rTMS over the left DLPFC in the rest period between the presentations of the Sternberg task; TMS + WM −, HF rTMS over the left DLPFC without a cognitive load; TMS − WM + (maintenance), HF rTMS over the vertex during maintenance period of the Sternberg task.
Figure 3
Figure 3
Example of the stimulation target for rTMS over left DLPFC in a healthy volunteer.
See this image and copyright information in PMC

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