Continuous theta-burst stimulation over the right dorsolateral prefrontal cortex impairs visuospatial working memory performance in medium load task

Abstract

Previous studies have shown that visuospatial working memory (VSWM) plays a key role in the encoding and processing of visuospatial information. More importantly, there is evidence suggesting the role of frontal and parietal cortical areas in VSWM and especially, the influence of the frontal cortex in regulating goal-directed behavior. However, the functional role of the right dorsolateral prefrontal cortex (rDLPFC) in visuospatial working memory is still unclear. Here, we noninvasively modulated the rDLPFC activity using continuous thetaburst stimulation (cTBS), with the vertex as the control site. Our study aimed to investigate the effects of cTBS over rDLPFC on working memory task (2-and 4-back) performance. Working memory performance was assessed at the baseline and after stimulation. We observed that the working memory performance as measured by discriminability index was impaired after cTBS over rDLPFC in 2-back task, whereas 4-back task performance was not significantly affected. More so, there was no effect on performance after cTBS over the vertex, suggesting a functional role of rDLPFC in VSWM. Our findings demonstrate the involvement of the rDLPFC in VSWM as well as the load-dependent effect of working memory performance. Taken together, our work constitutes a useful addition to the literature and underscores the effectiveness and efficiency of noninvasive brain stimulation in modulating neurocognitive activity.

Enhancing Visuospatial Working Memory Performance Using Intermittent Theta-Burst Stimulation Over the Right Dorsolateral Prefrontal Cortex

“…For this reason, the purpose of measuring the AMT of each participant was to ensure that 40% of MSO did not surpass the individual’s stimulation tolerance level and hence enhanced participants’ safety. Besides, the application of uniform stimulation intensity is consistent with the previous studies including Ott et al (2011) ; Vékony et al (2018) , and our recent cTBS study ( Ngetich et al, 2021 ). All the participants gave written informed consent before they began the experiment and were given monetary compensation at the end of the experiment.…”

“…This was informed by the limitation in the stimulator’s maximal TBS intensity. Nevertheless, applying uniform stimulation intensity has been used previously to study the functional roles of different cortical brain areas ( Ott et al, 2011 ; Kiyonaga et al, 2014 ; Vékony et al, 2018 ; Ngetich et al, 2021 ). The MNI coordinates (x = 43, y = 41, and z = 34) for the rDLPFC were similar to those used by Fried et al (2014) , which correspond to the right middle frontal gyrus ( Petrides, 2019 ).…”

“…Furthermore, the extant literature suggests that continuous theta-burst stimulation (cTBS) over the left DLPFC decreases verbal WM task performance ( Schicktanz et al, 2015 ; Vékony et al, 2018 ). While, our previous study using the visuospatial n-back task, found that applying cTBS over the right DLPFC impairs performance in a 2-back task ( Ngetich et al, 2021 ). On the other hand, a study using the verbal WM n-back task indicates that iTBS over the left DLPFC enhances working memory performance ( Hoy et al, 2015 ).…”

“…The findings of the present study would greatly contribute to the growing literature on the cognitive effects of TBS over the focal brain areas. Additionally, the evidence that iTBS is efficacious as a treatment complement to pharmacotherapy in refractory neuropsychiatric disorders such as depression ( Plewnia et al, 2014 ; Cheng et al, 2016 ; Ngetich et al, 2021 ), makes this study even more crucial.…”

“…More studies are thus required to verify whether the iTBS cortical modulation necessarily potentiates behavioral performance. Since most studies indicate that iTBS upregulate cortical activity ( Wischnewski and Schutter, 2015 ; Chung et al, 2017 , 2018a , b ; Lowe et al, 2018 ) and DLPFC is implicated in WM ( Rottschy et al, 2012 ; Hoy et al, 2015 ; Vékony et al, 2018 ; Ngetich et al, 2021 ), the present study sought to establish the behavioral impact of iTBS over the rDLPFC on VSWM.…”