Transcranial electrical stimulation and the neural dynamics of consciousness

意识的神经相关物（NCC）已经被认真研究了大约三十年。知觉意识被发现与不同频率的神经元振荡的调制密切相关，但很难确定特定大脑区域的振荡是否与该区域计算的内容的意识有关。我们需要的是一个证明，在特定的大脑区域的神经振荡的调制是否会影响的可能性计算的内容达到意识的区域。我建议在双眼闪光抑制，后对比掩蔽，特罗克斯勒消失，和操纵曝光时间的脑电刺激实验。这种范式有助于识别NCC，因为它揭示了当刺激被有意识地感知时与没有被感知时相比，存在哪些神经活动。例如，一项元对比掩蔽研究表明，当相同的掩蔽目标是可见的而不是不可见的时，EEG振荡功率、（头皮）电极间相位同步和ERP更大。我的实验室显示，当双眼竞争中的意识感知发生变化时，相关大脑区域的网络中的伽马功率和区域间相位同步以及θ-伽马交叉频率耦合都会增加。在我的实验室对特罗克斯勒消失的研究中，我们发现，当改变对比度的外周环保留在感知中时，比当它消失时，额顶叶相位同步和传递熵更大。我建议调制相关的振荡频率直接使用经颅电刺激（tES）以各种方式在性能的意识变化的范例。tES已经显示出调节神经振荡，这两者都是间接地通过增加兴奋性（例如，经颅直流电刺激，tDCS，经颅随机噪声刺激，tRNS）和直接驱动振荡（经颅交流电刺激，tACS）。交叉频率tACS已被用来证明空间工作记忆对θ（6 Hz）和高伽马（80-100 Hz）振荡同步的依赖性。同样，我建议确定依赖的视觉刺激的有意识的感知信息流（相位同步和传递熵）内的相关大脑网络。我做了一个实验，在特罗克斯勒消失的过程中，我用阳极或阴极tDCS刺激楔前叶。我们观察两种情况之间的行为差异，现在将使用EEG来研究行为差异是否伴随着早期EEG研究中确定的额顶叶区域之间的锁相值和/或传递熵的变化。在其他研究中，我将使用高清晰度tACS直接调制所涉及的振荡频率，以便做出更直接和精确的因果推断。

The neural correlates of consciousness (NCCs) have been under serious investigation for about three decades. Perceptual consciousness has been found to be strongly associated with modulations of neuronal oscillations at various frequencies, but it has been difficult to ascertain whether the oscillations in a particular brain region are causal for consciousness of the content computed by that region. What is needed is a demonstration that modulation of the neural oscillations in a particular brain region either does or does not affect the likelihood of the content computed by that region of reaching consciousness. I propose electrical brain stimulation experiments in binocular flash suppression, metacontrast masking, Troxler vanishing, and manipulating exposure duration. Such paradigms help identify the NCCs by exposing what neural activity is present when the stimuli are perceived consciously compared with when they are not. For example, one metacontrast masking study showed that EEG oscillatory power, inter-(scalp)electrode phase synchrony, and ERPs were larger when the same masked target was visible versus invisible. My lab showed increases in gamma power and inter-regional phase synchrony, as well as theta-gamma cross-frequency coupling, in a network of relevant brain areas around the time when a conscious percept in binocular rivalry changed. In a study of Troxler vanishing from my lab, we found greater frontal-parietal phase synchronization and transfer entropy when a peripheral annulus that changed contrast remained in perception than when it vanished. I propose modulating the relevant oscillatory frequencies directly using transcranial electrical stimulation (tES) in various ways during performance in consciousness-varying paradigms. tES has been shown to modulate neural oscillations, both indirectly by increasing excitability (e.g., trans-cranial direct current stimulation, tDCS, trans-cranial random noise stimulation, tRNS) and by driving the oscillations directly (trans-cranial alternating current stimulation, tACS). Cross-frequency tACS has been used to demonstrate the dependence of spatial working memory on synchronization of theta (6 Hz) and high gamma (80-100 Hz) oscillations. Similarly, I propose to determine the dependence of conscious perception of visual stimuli on information flow (phase synchrony and transfer entropy) within the relevant brain networks. I have run an experiment in which I stimulated the precuneus with either anodal or cathodal tDCS during Troxler vanishing. We observe behavioural differences between the two conditions and will now use EEG to investigate whether the behavioural difference is accompanied by changes in phase locking value and/or transfer entropy between the frontal-parietal regions identified in the earlier EEG study. In other studies I will use high definition tACS to directly modulate the oscillatory frequencies involved, in order to make more direct and precise causal inferences.