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

• Main Authors: Ilya Bakulin, Alfiia Zabirova, Dmitry Lagoda, Alexandra Poydasheva, Anastasiia Cherkasova, Nikolay Pavlov, Peter Kopnin, Dmitry Sinitsyn, Elena Kremneva, Maxim Fedorov, Elena Gnedovskaya, Natalia Suponeva, Michael Piradov
• Format: Article
• Language: English
• Published: MDPI AG 2020-02-01
• Series: Brain Sciences
• Subjects: working memory; non-invasive brain stimulation; transcranial magnetic stimulation; neuromodulation; cognitive function; cognitive training; n-back task; dorsolateral prefrontal cortex; cognitive enhancement
• Online Access: https://www.mdpi.com/2076-3425/10/2/83

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.