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

Abstract

Noninvasive brain stimulation provides a promising approach for the treatment of neuropsychiatric conditions. Despite the increasing research on the facilitatory effects of this kind of stimulation on the cognitive processes, the majority of the studies have used the standard stimulation approaches such as the transcranial direct current stimulation and the conventional repetitive transcranial magnetic stimulation (rTMS) which seem to be limited in robustness and the duration of the transient effects. However, a recent specialized type of rTMS, theta-burst stimulation (TBS), patterned to mimic the natural cross-frequency coupling of the human brain, may induce robust and longer-lasting effects on cortical activity. Here, we aimed to investigate the effects of the intermittent TBS (iTBS), a facilitatory form of TBS, over the right DLPFC (rDLPFC), a brain area implicated in higher-order cognitive processes, on visuospatial working memory (VSWM) performance. Therefore, iTBS was applied over either the rDLPFC or the vertex of 24 healthy participants, in two separate sessions. We assessed VSWM performance using 2-back and 4-back visuospatial tasks before iTBS (at the baseline (BL), and after the iTBS. Our results indicate that the iTBS over the rDLPFC significantly enhanced VSWM performance in the 2-back task, as measured by the discriminability index and the reaction time. However, the 4-back task performance was not significantly modulated by iTBS. These findings demonstrate that the rDLPFC plays a critical role in VSWM and that iTBS is a safe and effective approach for investigating the causal role of the specific brain areas.

Prolonged Intermittent Theta Burst Stimulation Targeting the Left Prefrontal Cortex and Cerebellum Does Not Affect Executive Functions in Healthy Individuals

“…Despite a large sample size and a randomised sham-controlled cross-over design, we did not nd evidence that prolonged iTBS over the LDLPFC induced behavioural or neuropsychological effects on working memory and cognitive control. This nding is in contrast with other studies which have reported signi cant behavioural effects with active rTMS targeting LDLPFC on such measures 30,[59][60][61] . It is possible that methodological differences between studies (e.g., rTMS parameters, EEG and ERP processing methods) may potentially explain discrepancies in ndings.…”

Prolonged intermittent theta burst stimulation targeting the left prefrontal cortex and cerebellum does not affect executive functions in healthy individuals

“…Despite a large sample size and a randomised sham-controlled cross-over design, we did not find evidence that prolonged iTBS over the LDLPFC induced behavioural or neuropsychological effects on working memory and cognitive control. This finding is in contrast with other studies that have reported significant behavioural effects with active rTMS targeting LDLPFC on such measures 31,33,69,70 . It is possible that methodological differences between studies (e.g., rTMS parameters, EEG and ERP processing methods) may explain discrepancies in findings.…”