FV 6 Sustained GABA reduction induced by anodal Transcranial direct current stimulation (tDCS) in motor cortex – a proton magnetic resonance spectroscopy study

Abstract

Background Transcranial direct current stimulation (tDCS) is a non-invasive technique that modulates excitability of neurons in the cerebral cortex. Anodal tDCS has been reported to modulate the activation of motor cortex as well as GABA concentration in motor cortex ( Nitsche and Paulus, 2000 ). Objective To date very little is known about the nature and duration of tDCS induced effects. We aimed to investigate long-term effects of anodal tDCS on the primary motor cortex (M1). Repeated magnetic resonance spectroscopy (MRS) was employed to measure relative gamma-aminobutyric acid concentrations in M1 up to 60 min after stimulation. Materials and methods Twenty right-handed healthy volunteers were recruited in RWTH Aachen University. 1 mA anodal and sham tDCS were applied for 10 min, respectively. MRS scans were performed before and after stimulation on a 3T Siemens PRISMA whole-body scanner, GABA-edited spectra were acquired from a volume of interest of 3 × 3 × 3 cm (27 mL) carefully placed on the hand area of the left M1 ( Fig. 1 ). MEGA-PRESS J-editing ( Mescher et al., 1998 ) was used for GABA detection. Data processing and quantification of spectra was performed with TARQUIN ( Wilson et al., 2011 ). Results An ANOVA was performed on GABA concentrations with stimulation (sham vs. anodal) and measurement (12 measurements: 2 pre-stimulation and 10 post-stimulation measurements) as between- and within-participants factors, respectively. The main effects of stimulation and measurements were significant F (1, 18) = 9.200, p = .007 and F (11, 198) = 2.354, p = .010. Crucially, the interaction was significant F (11, 198) = 3.089, p Fig. 2 ). In other words, GABA signal showed no change over time in the sham group, whereas it decreased significantly in the anodal group and stayed at about the same level across the whole planned test measurements over 86 min. Discussion and conclusion Such a long-lasting (over 86 min) decrease in GABA concentration corresponds not only to the reported behavioral effects of tDCS stimulation, such as increased motor learning capacity, but also, to the timeline of increased brain energy consumption following anodal tDCS as measured with Phosphorus spectroscopy ( Binkofski et al., 2011 ). Our results are relevant for the understanding of the mechanism of motor cortical plasticity and neuropsychiatric diseases in humans.