Institute of Cognitive Neuroscience, University College London, UK; Department of Psychology, Univeristy of Westminster, UK.
Institute of Cognitive Neuroscience, University College London, UK.
Neuropsychologia. 2019 May;128:332-339. doi: 10.1016/j.neuropsychologia.2018.03.030. Epub 2018 Apr 6.
Transcranial direct current stimulation (tDCS) and transcranial random noise stimulation (tRNS) have been claimed to produce many remarkable enhancements in perception, cognition, learning and numerous clinical conditions. The physiological basis of the claims for tDCS rests on the finding that 1 mA of unilateral anodal stimulation increases cortical excitation and 1 mA of cathodal produces inhibition. Here we show that these classic excitatory and inhibitory effects do not hold for the bilateral stimulation or 2 mA intensity conditions favoured in cognitive enhancement experiments. This is important because many, including some of the most salient claims are based on experiments using 2 mA bilateral stimulation. The claims for tRNS are also based on unilateral stimulation. Here we show that, again the classic excitatory effects of unilateral tRNS do not extend to the bilateral stimulation preferred in enhancement experiments. Further, we show that the effects of unilateral tRNS do not hold when one merely doubles the stimulation duration. We are forced to two conclusions: (i) that even if all the data on TES enhancements are true, the physiological explanations on which the claims are based are at best not established but at worst false, and (ii) that we cannot explain, scientifically at least, how so many experiments can have obtained data consistent with physiological effects that may not exist.
经颅直流电刺激（tDCS）和经颅随机噪声刺激（tRNS）据称可在感知、认知、学习和许多临床病症方面产生显著的增强效果。tDCS 声称的生理学基础基于这样一个发现，即 1mA 的单侧阳极刺激可增加皮质兴奋，而 1mA 的阴极刺激则产生抑制。在这里，我们表明这些经典的兴奋和抑制作用不适用于在认知增强实验中首选的双侧刺激或 2mA 强度条件。这很重要，因为许多（包括一些最突出的主张）都是基于使用 2mA 双侧刺激的实验。tRNS 的主张也是基于单侧刺激。在这里，我们表明，同样，单侧 tRNS 的经典兴奋作用也不会扩展到增强实验中首选的双侧刺激。此外，我们还表明，当仅仅将刺激持续时间延长一倍时，单侧 tRNS 的作用就不复存在了。我们被迫得出两个结论：（i）即使所有关于 TES 增强的数据都是真实的，那么基于这些主张的生理学解释最多是尚未确立，最坏的情况是错误的；（ii）从科学的角度来看，我们无法解释为什么如此多的实验能够获得与可能不存在的生理效应一致的数据。
