Abstract
Motor participation in phonological processing can be modulated by task nature across the speech perception to speech production range. The pars opercularis of the left inferior frontal gyrus (LIFG) would be increasingly active across this range, because of changing motor demands. Here, we investigated with simultaneous tDCS and fMRI whether the task load modulation of tDCS effects translates into predictable patterns of functional connectivity. Findings were analysed under the “multi-node framework”, according to which task load and the network structure underlying cognitive functions are modulators of tDCS effects. In a within-subject study, participants (N = 20) performed categorical perception, lexical decision and word naming tasks [which differentially recruit the target of stimulation (LIFG)], which were repeatedly administered in three tDCS sessions (anodal, cathodal and sham). The LIFG, left superior temporal gyrus and their right homologues formed the target network subserving phonological processing. C-tDCS inhibition and A-tDCS excitation should increase with task load. Correspondingly, the larger the task load, the larger the relevance of the target for the task and smaller the room for compensation of C-tDCS inhibition by less relevant nodes. Functional connectivity analyses were performed with partial correlations, and network compensation globally inferred by comparing the relative number of significant connections each condition induced relative to sham. Overall, simultaneous tDCS and fMRI was adequate to show that motor participation in phonological processing is modulated by task nature. Network responses induced by C-tDCS across phonological processing tasks matched predictions. A-tDCS effects were attributed to optimisation of network efficiency.
Highlights
Transcranial direct current stimulation is a brain stimulation tool that has been widely used in research with humans (Nitsche et al 2008)
The present study aimed to investigate with simultaneous Transcranial direct current stimulation (tDCS) and fMRI whether the task load modulation of tDCS effects observed behaviourally in Rodrigues de Almeida et al (2019) for motor participation in phonological processing translates into a predictable pattern of functional network connectivity
A 2 × 4 linear mixed effect model was fitted to the mean parameter estimates of regions of interest (ROIs) activation data of both anodal and cathodal tDCS conditions
Summary
Transcranial direct current stimulation (tDCS) is a brain stimulation tool that has been widely used in research with humans (Nitsche et al 2008). It still yields inconsistent results across studies, especially in those studying cognition (Jacobson et al 2012). We call the “multi-node framework”, the relevance of two aspects in particular, namely task load and the network structure underlying cognitive functions. In Meinzer’s work, neuroimaging with fMRI showed that only the brain region underlying the most challenging aspect of the task responded to tDCS, despite
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