Cognitive Aftereffects of Acute tDCS Coupled with Cognitive Training: An fMRI Study in Healthy Seniors

Abstract

Enhancing cognitive functions through noninvasive brain stimulation is of enormous public interest, particularly for the aging population in whom processes such as working memory are known to decline. In a randomized double-blind crossover study, we investigated the acute behavioral and neural aftereffects of bifrontal and frontoparietal transcranial direct current stimulation (tDCS) combined with visual working memory (VWM) training on 25 highly educated older adults. Resting-state functional connectivity (rs-FC) analysis was performed prior to and after each stimulation session with a focus on the frontoparietal control network (FPCN). The bifrontal montage with anode over the left dorsolateral prefrontal cortex enhanced VWM accuracy as compared to the sham stimulation. With the rs-FC within the FPCN, we observed significant stimulation × time interaction using bifrontal tDCS. We found no cognitive aftereffects of the frontoparietal tDCS compared to sham stimulation. Our study shows that a single bifrontal tDCS combined with cognitive training may enhance VWM performance and rs-FC within the relevant brain network even in highly educated older adults.

Modulation of network centrality and gray matter microstructure using multi‐session brain stimulation and memory training

“…In fact, studies that probed task‐related neural activity during application of anodal tDCS over functionally relevant brain regions have shown modulations on the network level (Holland et al, 2016 ; Martin et al, 2017 ). Investigation of changes in resting‐state networks after a single session of either anodal or bilateral tDCS over task‐relevant brain areas further demonstrated its potential to modulate functional connectivity (Meinzer et al, 2013 ; Sehm et al, 2012 ; Šimko et al, 2021 ). Indeed, anodal tDCS may induce cortical excitability changes in activated networks, as demonstrated in studies assessing transcranial magnetic stimulation‐evoked potentials using electroencephalography (Pellicciari et al, 2013 ; Pisoni et al, 2018 ; Romero Lauro et al, 2014 ).…”

“…Thus, while there is some evidence from single‐session tDCS studies (Meinzer et al, 2013 ; Pisoni et al, 2018 ; Sehm et al, 2012 ; Šimko et al, 2021 ), and first evidence from multi‐session tDCS studies (Antonenko, Külzow, De Sousa, et al, 2018 ; Möller et al, 2017 ) for functional network effects in human participants, whether microstructural plasticity changes accompany tDCS plus training‐related interventions is not fully understood. This knowledge on microstructural plasticity after multi‐session tDCS is crucial, however, given the potential of these approaches to induce long‐lasting neural plasticity (cf., Abellaneda‐Pérez et al, 2019 ).…”

“…ECM not only accounts for direct connections, but can be used to identify "hubs" or "nodes" that are of high importance or prominence in a network (Lohmann et al, 2010;Wink et al, 2012), similar to Google's "PageRank" algorithm (cf., Wink et al, 2012). Other approaches for assessment of functional network connectivity, such as Independent Component Analysis (ICA; Smith et al, 2009), require a priori decisions, for example on the number of components as well as the network of interest (such as default mode network (DMN) or executive control network, among others). We thus chose ECM as the optimal approach to measure centrality on the whole-brain level not requiring a priori assumptions while forgoing the high computational demands of other graph analytic methods (Joyce et al, 2010;Lohmann et al, 2010;Wink et al, 2012).…”

Inter-individual differences in baseline dynamic functional connectivity are linked to cognitive aftereffects of tDCS

“…However, the effectiveness in maintaining cognitive functions varies greatly both across and within intervention types 13 .Transcranial direct-current stimulation (tDCS) was proposed as an inexpensive and easily administered method for experimental use, and potentially also for clinical use, in an attempt to modulate cognitive functions 14 . Research aiming to modulate cognition using tDCS suggests that ongoing brain processing can be tuned and reorganized on the level of large-scale brain networks 15,16 , resulting in a favorable behavioral aftereffect via improved inter-and intra-network communication [17][18][19][20][21] . tDCS applies a weak direct electric current through two electrodes placed over the scalp with the goal of modulating underlying cortical excitability 22 .…”

Efficacy of Transcranial Direct Current Stimulation Over Dorsolateral Prefrontal Cortex in Patients With Minimally Conscious State

“…A decreased functional connectivity was found in left and right default modes, executive control, auditory, and attention networks in patients with MCS (33,34). Previous studies in healthy participants showed that tDCS over left DLPFC could increase the FC between the left DLPFC and bilateral parietal regions (5,35). Our findings showed that an increased FC in sensorimotor network (bilateral supplementary motor area), frontal parietal network (right angular gyrus), and auditory network (right superior temporal gyrus) post-2-week real tDCS, which provided another piece of evidence that improvement of FC in both nearby and distant of the stimulated brain regions could be induced by tDCS in patients with MCS (5,(36)(37)(38)(39).…”