Journal
JOURNAL OF NEUROSCIENCE
Volume 37, Issue 15, Pages 4065-4073Publisher
SOC NEUROSCIENCE
DOI: 10.1523/JNEUROSCI.0079-17.2017
Keywords
aging; magnetic resonance spectroscopy; plasticity; sensorimotor network; transcranial electrical stimulation
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Funding
- Bundesministerium fur Bildung und Forschung [01GQ1424A]
- German-Israeli Foundation for Scientific Research and Development [I-1299-105.4/2015]
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Transcranial direct current stimulation (tDCS) modulates human behavior, neuronal patterns, and metabolite concentrations, with exciting potential for neurorehabilitation. However, the understanding of tDCS-induced alterations on the neuronal level is incomplete, and conclusions from young adults, in whom the majority of studies have been conducted, cannot be easily transferred to older populations. Here, we investigated tDCS-induced effects in older adults (N = 48; age range, 50-79 years) using magnetic resonance spectroscopy to quantify GABA levels as well as resting-state functional magnetic resonance imaging to assess sensorimotor network strength and interhemispheric connectivity. In a randomized, counterbalanced, crossover design, we applied anodal tDCS (atDCS), cathodal tDCS (ctDCS), and sham tDCS (stDCS) over the left sensorimotor region. We observed a significant reduction of GABA levels after atDCS compared with stDCS, reflecting the preserved neuromodulatory effect of atDCS in older adults. Moreover, resting-state functional coupling was decreased during atDCS compared with stDCS, most likely indicating augmented efficiency in brain network functioning. Increased levels of interhemispheric connectivity with age were diminished by atDCS, suggesting stimulation-induced functional decoupling. Further, the magnitude of atDCS-induced local plasticity was related to baseline functional network strength. Our findings provide novel insight into the neuronal correlates underlying tDCS-induced neuronal plasticity in older adults and thus might help to develop tDCS interventions tailored to the aging brain.
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