No Effects of Anodal tDCS on Local GABA and Glx Levels in the Left Posterior Superior Temporal Gyrus

Abstract

A number of studies investigating the biological effects of transcranial direct current stimulation (tDCS) using magnetic resonance spectroscopy (MRS) have found that it may affect local levels of γ-aminobutyric acid (GABA), glutamate and glutamine (commonly measured together as “Glx” in spectroscopy), and N-acetyl aspartate (NAA), however, these effects depend largely on the stimulation parameters used and the cortical area targeted. Given that different cortical areas may respond to stimulation in different ways, the purpose of this experiment was to assess the as yet unexplored biological effects of tDCS in the posterior superior temporal gyrus (pSTG), an area that has attracted some attention as a potential target for the treatment of auditory verbal hallucinations in schizophrenia patients. Biochemical changes were monitored using continuous, online MRS at a field strength of 3 Tesla. Performing intrascanner stimulation, with continuous spectroscopy before, during and after stimulation, permitted the assessment of acute effects of tDCS that would otherwise be lost when simply comparing pre- and post-stimulation differences. Twenty healthy participants underwent a repeated-measures experiment in which they received both active anodal and sham intrascanner stimulation in a stratified, randomized, double-blind experiment. No significant changes in GABA, Glx, or NAA levels were observed as a result of anodal stimulation, or between active and sham stimulation, suggesting that a single session of anodal tDCS to the pSTG may be less effective than in other cortical areas that have been similarly investigated.

Effects of Transcranial Direct Current Stimulation on GABA and Glx in Children: A pilot study

“…While this cannot be confirmed in our investigation, there is literature suggesting changes in GABA concentration are time sensitive with fluctuation in GABA concentration occurring in the 90 minute window following stimulation [4,55,65]. The time sensitivity of metabolite measurements is further supported by seemingly discrepant findings in the literature in which GABA and Glx changes are not seen during tDCS [66][67][68].…”

Effects of Transcranial Direct Current Stimulation on GABA and Glutamate in Children: A Pilot Study

“…While this cannot be confirmed in our investigation, there is literature suggesting changes in GABA concentration are time sensitive with fluctuation in GABA concentration occurring in the 90 minute window following stimulation (4,46,57). The time sensitivity of metabolite measurements is further supported by seemingly discrepant findings in the literature in which GABA and Glx changes are not seen during tDCS (58)(59)(60).…”

Effects of bifrontal transcranial direct current stimulation on brain glutamate levels and resting state connectivity: multimodal MRI data for the cathodal stimulation site

“…Despite its relevance as a conceptual pilot project, our study has obvious limitations that need to be considered when interpreting the data. As said, the sample size is critically low, which is even more problematic at the subgroup level (defined by gender or efield parameters); however, it is comparable with sample sizes in previous tDCS-MRS studies (e.g., N = 17 in Hone-Blanchet et al [40], N = 12 in Bachtiar et al [38], N = 20 in Dwyer et al [78], N = 24 in Antonenko et al [37]). Thus, larger trials are clearly missing in the field.…”