Neuromodulatory effects of transcranial magnetic stimulation on language performance in healthy participants: Systematic review and meta-analysis

Abstract

BackgroundThe causal relationships between neural substrates and human language have been investigated by transcranial magnetic stimulation (TMS). However, the robustness of TMS neuromodulatory effects is still largely unspecified. This study aims to systematically examine the efficacy of TMS on healthy participants’ language performance.MethodsFor this meta-analysis, we searched PubMed, Web of Science, PsycINFO, Scopus, and Google Scholar from database inception until October 15, 2022 for eligible TMS studies on language comprehension and production in healthy adults published in English. The quality of the included studies was assessed with the Cochrane risk of bias tool. Potential publication biases were assessed by funnel plots and the Egger Test. We conducted overall as well as moderator meta-analyses. Effect sizes were estimated using Hedges’g (g) and entered into a three-level random effects model.ResultsThirty-seven studies (797 participants) with 77 effect sizes were included. The three-level random effects model revealed significant overall TMS effects on language performance in healthy participants (RT: g = 0.16, 95% CI: 0.04–0.29; ACC: g = 0.14, 95% CI: 0.04–0.24). Further moderator analyses indicated that (a) for language tasks, TMS induced significant neuromodulatory effects on semantic and phonological tasks, but didn’t show significance for syntactic tasks; (b) for cortical targets, TMS effects were not significant in left frontal, temporal or parietal regions, but were marginally significant in the inferior frontal gyrus in a finer-scale analysis; (c) for stimulation parameters, stimulation sites extracted from previous studies, rTMS, and intensities calibrated to the individual resting motor threshold are more prone to induce robust TMS effects. As for stimulation frequencies and timing, both high and low frequencies, online and offline stimulation elicited significant effects; (d) for experimental designs, studies adopting sham TMS or no TMS as the control condition and within-subject design obtained more significant effects.DiscussionOverall, the results show that TMS may robustly modulate healthy adults’ language performance and scrutinize the brain-and-language relation in a profound fashion. However, due to limited sample size and constraints in the current meta-analysis approach, analyses at a more comprehensive level were not conducted and results need to be confirmed by future studies.Systematic review registration[https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=366481], identifier [CRD42022366481].

Transcranial Photobiomodulation on the Left Prefrontal Cortex Enhances Mandarin Chinese L1 and L2 Complex Sentence Processing Performances

“…Although adults’ language network is fully mature in both structure and function, it also appears to remain plastic during the whole lifespan in the course that we continue to learn and process various kinds of language information (either in L1 or L2; Li et al, 2014; Schlegel et al, 2012; Stein et al, 2012; Wang P. et al, 2021). Moreover, healthy adults with relatively small individual variance compared to patients can serve as an ideal case to explore NIBS’s modulatory effects (Hartwigsen et al, 2013; Qu Xin. et al, 2022).…”

“…It is worth noting that a large body of tES and TMS studies were interested in the explorations of the causal relationships between the target regions and the behavioral/neural changes in healthy participants by utilizing inhibitory protocols (e.g., Sakreida et al, 2019; Ware et al, 2021; Zhu & Snowman, 2020) while leaving the facilitatory/enhancement effects underspecified. A recent meta-analysis also pointed out that the modulation effectiveness of TMS on specific aspects of language ability (e.g., syntactic ability) was relatively limited (Qu Xin. et al, 2022).…”

“…In order to detect the tPBM effect on sentence processing, healthy adults who are native speakers of the target language with relatively small individual variance (compared to L2 learners with higher internal variance considering their differed language background, L2 proficiency level, age of acquisition, etc.) can serve as an ideal case and a starting point for the initial exploration (Hartwigsen et al, 2013; Qu Xin. et al, 2022).…”

Continuous Theta-Burst Stimulation on the Left Posterior Inferior Frontal Gyrus Perturbs Complex Syntactic Processing Stability in Mandarin Chinese

“…Across the last decades, as an effective noninvasive brain stimulation technique, transcranial magnetic stimulation (TMS) has increasingly been used to probe causal structure–function relationships with a high spatial resolution (e.g., Hallett, 2000 ; Hartwigsen, 2015 ; Hartwigsen & Silvanto, 2023 ; Qu et al, 2022 ; Uddén et al, 2017 ). Several studies have investigated the causal role of LpIFG with various syntactic tasks, as summarized in Table 1 .…”

“…Specifically, d ′ serves as a reliable indicator of processing quality ( Pinet & Nozari, 2021 ) because it reflects the ability to discriminate between signal and noise ( Stanislaw & Todorov, 1999 ) and provides deeper insights than mere accuracy rates ( Kuhl et al, 2005 ; Tolentino & Tokowicz, 2014 ). Moreover, reaction time (RT) is utilized as a processing quality measure due to its direct assessment of response speed to stimuli ( Buccino et al, 2005 ; Gough et al, 2005 ), providing an immediate gauge of cognitive processing and capturing the impact of TMS ( Qu et al, 2022 ). Additionally, the coefficient of variation (CV) is considered to reflect the degree of automation as it measures response variation—with less variation suggesting greater stability and automation ( Lim & Godfroid, 2015 ; Segalowitz & Hulstijn, 2005 ; Segalowitz & Segalowitz, 1993 ).…”