Impact of transcranial direct current stimulation on structural plasticity of the somatosensory system

Abstract

While there is a growing body of evidence regarding the behavioral and neurofunctional changes in response to the longitudinal delivery of transcranial direct current stimulation (tDCS), there is limited evidence regarding its structural effects. Therefore, the present study was intended to investigate the effect of repeatedly applied anodal tDCS over the primary somatosensory cortex on the gray matter (GM) and white matter (WM) compartment of the brain. Structural tDCS effects were, moreover, related to effects evidenced by functional imaging and behavioral assessment. tDCS was applied over the course of 5 days in 25 subjects with concomitant assessment of tactile acuity of the right and left index finger as well as imaging at baseline, after the last delivery of tDCS and at follow-up 4 weeks thereafter. Irrespective of the stimulation condition (anodal vs. sham), voxel-based morphometry revealed a behaviorally relevant decrease of GM in the precuneus co-localized with a functional change of its activity. Moreover, there was a decrease in GM of the bilateral lingual gyrus and the right cerebellum. Diffusion tensor imaging analysis showed an increase of fractional anisotropy exclusively in the tDCS condition in the left frontal cortex affecting the final stretch of a somatosensory decision making network comprising the middle and superior frontal gyrus as well as regions adjacent to the genu of the corpus callosum. Thus, this is the first study in humans to identify structural plasticity in the GM compartment and tDCS-specific changes in the WM compartment in response to somatosensory learning.

Microstructural and functional plasticity following repeated brain stimulation during cognitive training in older adults

“…However, as the control group did not receive any training, the results did not allow conclusions about whether effects were due to tDCS or training or both. Applying anodal tDCS over the left somatosensory cortex during repeated sensory learning, Hirtz and colleagues 61 found FA increases in anodal compared to sham group in the left frontal cortex, in the vicinity of the middle and superior frontal gyrus. The authors concluded that sensory learning involved prefrontal areas rather than stimulation target regions underneath the anodal electrode due to involvement of decision-making processes recruiting the frontoparietal network.…”

Therapeutic benefits of noninvasive somatosensory cortex stimulation on cortical plasticity and somatosensory function: A systematic review

“…Full-text articles were examined in cases of insufficient information in the title or abstract. In total, 73 full-text articles were screened for eligibility and 16 articles were removed for the following reasons: (1) primary outcome not assessed (Gundlach et al, 2017;Hornburger et al, 2019;Huh et al, 2016;Maddaluno et al, 2020;Zapallow et al, 2013); (2) primary outcome measured during rather than before and after NIBS (Manzo et al, 2020;Saito et al, 2021;Yokota et al, 2021); (3) primary outcome measured more than 24 h post-NIBS (Litvak et al, 2007); (4) SEPs measured from the lower limb (Zapallow et al, 2012); (5) NIBS not applied to the S1 (Uguisu et al, 2010); (6) number of participants for a given NIBS condition (dataset) < 5 (Sehm et al, 2013); (7) SEPs evoked by electrical stimulation only on the upper limb side ipsilateral to NIBS; (8) NIBS also administrated with repetitive tactile stimulation to induce S1 plasticity (Ragert et al, 2003); (9) SEP data filtered with a bandpass of 400-800 Hz to analyse high-frequency oscillations (Restuccia et al, 2007); and (10) data previously analysed by Hilgenstock et al (2016) (Hirtz et al, 2018). One additional article was added by the full-text assessment (Gatica Tossi et al, 2013).…”

Cerebellar Transcranial Direct Current Stimulation in Children with Developmental Coordination Disorder: A Randomized, Double-Blind, Sham-Controlled Pilot Study

“…However, this possibility is difficult to reconcile with evidence showing atDCS-induced structural changes in gray and white matter (Hirtz et al, 2018 ), which suggests that the effects of atDCS can outlast its time of application. Moreover, when learning is considered from a synaptic perspective (Baltaci et al, 2019 ), interventions that are presumed to facilitate synaptic plasticity should translate, at least partly, to enduring synaptic changes.…”