Author:

Keywords:

Science & Technology, Life Sciences & Biomedicine, Clinical Neurology, Neurosciences, Neurosciences & Neurology, Aging, Neuroplasticity, tDCS, MEP, TMS, Adolescent, Adult, Aged, Aged, 80 and over, Animals, Cortical Excitability, Cross-Over Studies, Evoked Potentials, Motor, Female, Humans, Long-Term Potentiation, Male, Middle Aged, Motor Cortex, Neuronal Plasticity, Single-Blind Method, Transcranial Direct Current Stimulation, Transcranial Magnetic Stimulation, Young Adult, 11 Medical and Health Sciences, Neurology & Neurosurgery, 32 Biomedical and clinical sciences, 42 Health sciences

Abstract:

BACKGROUND: Cognitive, and motor performance are reduced in aging, especially with respect to acquisition of new knowledge, which is associated with a neural plasticity decline. Animal models show a reduction of long-term potentiation, but not long-term depression, in higher age. Findings in humans are more heterogeneous, with some studies showing respective deficits, but others not, or mixed results, for plasticity induced by non-invasive brain stimulation. One reason for these heterogeneous results might be the inclusion of different age ranges in these studies. In addition, a systematic detailed comparison of the age-dependency of neural plasticity in humans is lacking so far. OBJECTIVE: We aimed to explore age-dependent plasticity alterations in adults systematically by discerning between younger and older participants in our study. METHODS: We recruited three different age groups (Young: 18-30, Pre-Elderly: 50-65, and Elderly: 66-80 years). Anodal, cathodal, or sham transcranial direct current stimulation (tDCS) was applied over the primary motor cortex with 1 mA for 15 min to induce neuroplasticity. Cortical excitability was monitored by single-pulse transcranial magnetic stimulation as an index of plasticity. RESULTS: For anodal tDCS, the results show a significant excitability enhancement, as compared to sham stimulation, for both, Young and the Pre-Elderly groups, while no LTP-like plasticity was obtained in the Elderly group by the applied stimulation protocol. Cathodal tDCS induced significant excitability-diminishing plasticity in all age groups. CONCLUSION: Our study provides further insight in age-related differences of plasticity in healthy humans, which are similar to those obtained in animal models. The decline of LTP-like plasticity in higher age could contribute to cognitive deficits observed in aging.