P 21. A 1H/31P MR spectroscopy study of GABA and high energy phosphates modulation induced by anodal tDCS in the primary motor cortex of healthy subjects

Introduction. Transcranial direct current stimulation (tDCS) is a non-invasive technique that modulates excitability of neurons in humans. Anodal tDCS has been used to investigate GABA concentration (Stagg et al 2009) and cerebral energy consumption in motor cortex (Binkofski et al 2011). To date very little is known about the effect of the duration of tDCS on cortical inhibition and related energy consumption or vice versa. We aim to explore long-term GABA and energy modulation following anodal tDCS on the primary motor cortex (M1) by repeated (1H) proton and (31P) phosphorus magnetic resonance spectroscopy (MRS) up to 60 minutes. Materials and Methods. Four righthanded healthy volunteers were recruited in RWTH Aachen University, Hospital Germany. All experiments were performed on a 3T Siemens PRISMA wholebody scanner using a 1H/31P head coil. One set of 1H GABA and 31P MRS scan and two sets of the same scans were carried out before and after the stimulation, respectively. 1 mA anodal and sham tDCS were applied for 20 minutes with the anodal electrode placed over the left M1 and cathodal electrode placed on the right supraorbital area. GABAedited 1H and 31P spectra were independently acquired from a volumeofinterest of 3x3x3cm (27mL) carefully localised on the left M1. MEGAPRESS Jediting was used for GABA detection (TR/TE = 5350/68 ms and 96 averages), and 3D CSI (TR/TE = 3730/2.3 ms and 6 averages) with NOE enhancement (Waltz4) was utilised for 31P acquisition. Data processing and quantification of GABA and 31P spectra were performed with LCModel and jMRUI software, respectively Results. Normalized GABA, ATP/Pi and PCr/Pi concentration from motor cortex following anodal tDCS are shown Figs. 1 and 2. The GABA signal shown in Fig. 1 increases immediately after anodal stimulation and remained increase until the end of the measurement. ATP/Pi and PCr/Pi ratios shown in Fig. 2 reduced following anodal tDCS and remained decrease until the end of measurement. Discussion and Conclusion. Our results revealed an increase of GABA concentration and decrease of 31P metabolites with increasing brain energy consumption following anodal tDCS as measured with 1H/31P MR Spectroscopy. Our preliminary results are relevant to understand the neurochemical mechanism underlying motor cortical plasticity and energy metabolism in humans. We intend to employ a large number of subjects in future for further analysis. References Stagg C. J., Best J. G., Stephenson M. C., O“Shea J., Wylezinska M., Kincses Z. T. Polarity-sensitive modulation of cortical neurotransmitters by transcranial stimulation. J. Neurosci. 2009;29(16) 5202–5206. Binkofski F, Loebig M, Jauch-Chara K, Bergmann S, Melchert UH, Scholand-Engler HG, Schweiger U, Pellerin L, Oltmanns KM. Brain energy consumption induced by electrical stimulation promotes systemic glucose uptake. Biol Psychiatry. 2011;70(7):690–5. Fig. 1. Fig. 2.