Proton Magnetic Resonance Spectroscopy of the motor cortex reveals long term GABA change following anodal Transcranial Direct Current Stimulation

Abstract

Anodal transcranial direct current stimulation (tDCS) over the primary motor cortex (M1) has been reported to increase the firing rates of neurons and to modulate the gamma-aminobutyric acid (GABA) concentration. To date, knowledge about the nature and duration of these tDCS induced effects is incomplete. We aimed to investigate long-term effects of anodal tDCS over M1 on GABA dynamics in humans. Repeated magnetic resonance spectroscopy (MRS) was employed to measure relative GABA concentration in M1 for approximately 64 minutes after stimulation. The study was performed on 32 healthy subjects. Either anodal or sham tDCS were applied for 10 minutes with the active electrode over the left M1 and the reference electrode over the right supra-orbital region. Pre and post-tDCS MRS scans were performed to acquire GABA-edited spectra using 3 T Prisma Siemens scanner. GABA signals showed no change over time in the sham tDCS group, whereas anodal tDCS resulted in a significant early decrease within 25 minutes after tDCS and then significant late decrease after 66 minutes which continued until the last test measurements. The late changes in GABA concentration might be related to long-term plasticity mechanism. These results contribute to a better understanding of the neurochemical mechanism underlying long-term cortical plasticity following anodal tDCS.

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

“…It is possible that subtle biphasic changes in GABA are taking place during motor learning that we are unable to detect. 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].…”

“…In this study, we suspect participants may have transitioned into a phase of learning that requires less plasticity and the cortex is no longer responding to tDCS with the predicted GABA and Glx changes at five days when our measures were taken. Adult literature suggests the changes in GABA and glutamate measured by MRS in response to learning vary with time [55,65] and it is possible that a ceiling of PPT skill, and also of metabolite change, was reached before our MRS measurements were taken.…”

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

“…It is possible that subtle biphasic changes in GABA are taking place during motor learning that we are unable to detect. 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).…”

“…In this study, we suspect participants may have transitioned into a phase of learning that requires less plasticity and the cortex is no longer responding to tDCS with the predicted GABA and Glx changes at five days when our measures were taken. Adult literature suggests the changes in GABA and glutamate measured by MRS in response to learning vary with time (46,57) and it is possible that a ceiling of PPT skill, and also of metabolite change, was reached before our MRS measurements were taken.…”

Therapeutic non-invasive brain stimulation in amyotrophic lateral sclerosis: rationale, methods and experience

“…Some MRS studies have demonstrated an increase in glutamate after anodal stimulation and decrease in glutamate after cathodal stimulation, although this has not been consistent in all studies. 36 37 More consistently, GABA has been shown to be decreased after both anodal and cathodal stimulation-and for at least 1 hour after anodal tDCS 38 leading to the suggestion of GABA as a gating factor whose reduction allows plastic changes to occur. The neurochemical basis of the tDCS after-effect also helps explain its variability, with multiple factors affecting neurochemical concentrations-such as alertness, sleep quality and caffeine-varying both within and between subjects.…”