P289 Induction of neuronal plasticity by transcranial direct current stimulation in healthy older adults

Abstract

Introduction Transcranial direct current stimulation (tDCS) has emerged as an efficient tool to enhance cognitive functioning in young as well as older adults. The underlying neuronal mechanisms, however, are still insufficiently understood. Especially studies investigating neuronal correlates of tDCS-induced plasticity in healthy older adults are rare. Objectives The objective of the study was to investigate the mechanisms underlying tDCS-induced neuronal modulation in a group of healthy older adults. In particular, alterations in resting state functional connectivity within the motor network as well as GABA concentration within the primary motor cortex were examined. Materials and methods In this study, we assessed the effects of anodal, cathodal, and sham tDCS over the left primary motor cortex on functional connectivity of the motor network and GABA concentration in a group of healthy older adults. Stimulation of 1 mA was applied for 15 min with anodal or cathodal polarity; for 30 s in sham stimulation. The three stimulation conditions were separated by at least one week and their order was counterbalanced across the group. GABA concentration was assessed by MRS using MEGA-PRESS at 3 T before and after the stimulation interval. Resting-state fMRI scans were obtained twice during stimulation, separated by a break of 3 min. Results In line with previous studies with young adults, GABA concentration change was lower in the anodal tDCS condition as compared to the sham tDCS condition. Resting state motor networks showed a reduced inter-hemispheric functional connectivity between left and right primary motor cortices during anodal tDCS compared to cathodal and sham tDCS. This observation is consistent with results in young and older adults that have assessed tDCS-induced alterations of inter-hemispheric functional connectivity during resting-state fMRI. Conclusion Our study demonstrates tDCS-induced neuronal plasticity in healthy older adults. This observed reorganization of the functional architecture of the motor cortex is in line with recent tDCS studies in young adults, however, research results are still heterogeneous. In sum, our data suggests that anodal tDCS induced a functional decoupling of motor cortices, indicating a reversal of age-related effects on inter-hemispheric connectivity.