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 1mA for 15 minutes 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.

中文翻译：

---

成人运动皮层可塑性的年龄相关差异：一项经颅直流电刺激研究

背景认知和运动能力随着年龄的增长而降低，尤其是在获得新知识方面，这与神经可塑性下降有关。动物模型显示，在较高年龄时，长期增强作用会降低，但不会出现长期抑郁。人类的研究结果更加异质，一些研究显示了各自的缺陷，但其他研究没有，或者结果混合，非侵入性脑刺激引起的可塑性。这些异质结果的原因之一可能是这些研究中包含了不同的年龄范围。此外，到目前为止，还缺乏对人类神经可塑性的年龄依赖性的系统详细比较。目标我们旨在通过在我们的研究中区分年轻和年长的参与者，系统地探索成人的年龄依赖性可塑性变化。方法 我们招募了三个不同的年龄组（年轻人：18-30 岁，老年人：50-65 岁，老年人：66-80 岁）。阳极、阴极或假经颅直流电刺激 (tDCS) 用 1mA 施加在初级运动皮层上 15 分钟以诱导神经可塑性。通过单脉冲经颅磁刺激监测皮质兴奋性作为可塑性指标。结果 对于阳极 tDCS，结果显示，与假刺激相比，青年组和老年组的兴奋性显着增强，而老年组通过应用的刺激方案没有获得类似 LTP 的可塑性。阴极 tDCS 在所有年龄组中诱导显着的兴奋性降低可塑性。结论我们的研究提供了对健康人类可塑性的年龄相关差异的进一步了解，这与在动物模型中获得的相似。较高年龄时 LTP 样可塑性的下降可能导致衰老过程中观察到的认知缺陷。