Nitsche Michael A, Roth Amelie, Kuo Min-Fang, Fischer Anja K, Liebetanz David, Lang Nicolas, Tergau Frithjof, Paulus Walter
Georg-August-University, Department for Clinical Neurophysiology, 37075 Goettingen, Germany.
J Neurosci. 2007 Apr 4;27(14):3807-12. doi: 10.1523/JNEUROSCI.5348-06.2007.
Associative neuroplasticity, which encompasses the modification of synaptic strength by coactivation of two synaptic inputs, has been linked to learning processes. Because unlimited plasticity destabilizes neuronal networks, homeostatic rules were proposed and experimentally proven that control for the amount and direction of plasticity dependent on background network activity. Accordingly, low background activity would enhance facilitatory plasticity, whereas high background activity would inhibit it. However, the impact of background excitability on associative plasticity has not been studied so far in humans. Facilitatory associative plasticity was induced by paired associative stimulation (PAS) in the human motor cortex, whereas background activity was enhanced or diminished by transcranial direct current stimulation (tDCS). When applied before PAS, excitability-enhancing tDCS also boosted the efficacy of PAS, whereas excitability-diminishing tDCS turned it into inhibition. Thus, previous background activity does not influence associative plasticity homeostatically. When tDCS and PAS were applied simultaneously, now in accordance with homeostatic rules of neuroplasticity, reduced background activity resulted in a prolonged excitability enhancement by PAS, whereas enhanced background activity turned it into inhibition. We conclude that background network activity can influence associative plasticity homeostatically. However, only simultaneous modulation of both parameters is in accordance with homeostatic concepts. These findings might be of importance for the development of plasticity-inducing stimulation protocols supporting information processing in humans.
联合神经可塑性，即通过两个突触输入的共同激活来修饰突触强度，已与学习过程相关联。由于无限的可塑性会破坏神经元网络的稳定性，因此提出了稳态规则并通过实验证明其可控制依赖于背景网络活动的可塑性的数量和方向。相应地，低背景活动会增强易化性可塑性，而高背景活动则会抑制它。然而，迄今为止尚未在人类中研究背景兴奋性对联合可塑性的影响。在人类运动皮层中，通过配对联合刺激（PAS）诱导易化性联合可塑性，而通过经颅直流电刺激（tDCS）增强或减弱背景活动。在PAS之前应用时，增强兴奋性的tDCS也会提高PAS的效果，而减弱兴奋性的tDCS则会使其变为抑制作用。因此，先前的背景活动不会以稳态方式影响联合可塑性。当同时应用tDCS和PAS时，现在根据神经可塑性的稳态规则，降低的背景活动会导致PAS引起的兴奋性增强延长，而增强的背景活动则会使其变为抑制作用。我们得出结论，背景网络活动可以以稳态方式影响联合可塑性。然而，只有同时调节这两个参数才符合稳态概念。这些发现可能对支持人类信息处理的可塑性诱导刺激方案的开发具有重要意义。
