Queensland Brain Institute, University of Queensland, St Lucia, QLD 4072, Australia; Cambridge Consciousness and Cognition Lab, Department of Psychology, University of Cambridge, Cambridge CB2 3EB, United Kingdom; Department of Biological and Experimental Psychology, School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom.
Queensland Brain Institute, University of Queensland, St Lucia, QLD 4072, Australia.
Neuroimage. 2020 Dec;223:117305. doi: 10.1016/j.neuroimage.2020.117305. Epub 2020 Aug 28.
Transcranial magnetic stimulation (TMS) has been widely used in human cognitive neuroscience to examine the causal role of distinct cortical areas in perceptual, cognitive and motor functions. However, it is widely acknowledged that the effects of focal cortical stimulation can vary substantially between participants and even from trial to trial within individuals. Recent work from resting state functional magnetic resonance imaging (fMRI) studies has suggested that spontaneous fluctuations in alertness over a testing session can modulate the neural dynamics of cortical processing, even when participants remain awake and responsive to the task at hand. Here we investigated the extent to which spontaneous fluctuations in alertness during wake-to-sleep transition can account for the variability in neurophysiological responses to TMS. We combined single-pulse TMS with neural recording via electroencephalography (EEG) to quantify changes in motor and cortical reactivity with fluctuating levels of alertness defined objectively on the basis of ongoing brain activity. We observed rapid, non-linear changes in TMS-evoked responses with decreasing levels of alertness, even while participants remained responsive in the behavioural task. Specifically, we found that the amplitude of motor evoked potentials peaked during periods of EEG flattening, whereas TMS-evoked potentials increased and remained stable during EEG flattening and the subsequent occurrence of theta ripples that indicate the onset of NREM stage 1 sleep. Our findings suggest a rapid and complex reorganization of active neural networks in response to spontaneous fluctuations of alertness over relatively short periods of behavioural testing during wake-to-sleep transition.
经颅磁刺激（TMS）已广泛应用于人类认知神经科学中，以研究不同皮质区域在感知、认知和运动功能中的因果作用。然而，人们普遍认为，皮质刺激的效果在不同个体之间甚至在个体内部的不同试验中都会有很大的差异。最近来自静息态功能磁共振成像（fMRI）研究的工作表明，在测试过程中警觉性的自发波动可以调节皮质处理的神经动力学，即使参与者保持清醒并对当前任务有反应。在这里，我们研究了在从清醒到睡眠过渡期间警觉性的自发波动在多大程度上可以解释对 TMS 的神经生理反应的可变性。我们将单脉冲 TMS 与通过脑电图（EEG）进行的神经记录相结合，以量化在警觉性波动的情况下运动和皮质反应性的变化，警觉性波动是根据持续的大脑活动客观定义的。我们观察到，即使参与者在行为任务中保持反应能力，随着警觉性的降低，TMS 诱发反应也会发生快速、非线性的变化。具体而言，我们发现运动诱发电位的幅度在 EEG 变平期间达到峰值，而 TMS 诱发电位在 EEG 变平期间以及随后出现表明 NREM 阶段 1 睡眠开始的 theta 涟漪期间增加并保持稳定。我们的研究结果表明，在从清醒到睡眠过渡期间的相对较短的行为测试期间，警觉性的自发波动会导致活跃神经网络的快速而复杂的重组。
