Transcranial electrical stimulation and the neural dynamics of consciousness

意识的神经关联（NCCs）已经被认真研究了大约三十年。知觉意识已被发现与不同频率的神经元振荡调制密切相关，但很难确定大脑特定区域的振荡是否与该区域计算的内容的意识有因果关系。我们需要证明的是，特定大脑区域的神经振荡的调节，会或不会影响由该区域计算的内容达到意识的可能性。我建议在双目闪光抑制、变反差掩蔽、特罗克斯勒消失和操纵曝光时间方面进行脑电刺激实验。这些范例通过揭示当刺激物被有意识地感知时与非有意识地感知时存在的神经活动来帮助识别ncc。例如，一项元对比掩蔽研究表明，当同一掩蔽目标可见时，脑电图振荡功率、（头皮）电极间相位同步和erp更大。我的实验室显示，当双眼竞争的意识感知发生变化时，大脑相关区域网络中的伽马能量和区域间相位同步以及θ - γ交叉频率耦合都有所增加。在一项关于Troxler从我的实验室消失的研究中，我们发现当改变对比度的外周环仍然存在时，比当它消失时，更大的额-顶叶相位同步和传递熵。我建议在意识变化范式的表现过程中，以各种方式直接使用经颅电刺激（tES）来调制相关的振荡频率。tES已被证明可以调节神经振荡，通过间接增加兴奋性（例如，经颅直流刺激，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已被用于证明空间工作记忆对theta （6 Hz）和高gamma （80-100 Hz）振荡同步的依赖性。同样，我建议确定视觉刺激的有意识感知对相关大脑网络中的信息流（相位同步和传递熵）的依赖。我做了一个实验，在特罗克斯勒消失期间我用正极或正极tDCS刺激楔前叶。我们观察了两种情况下的行为差异，现在将使用脑电图来研究这种行为差异是否伴随着早期脑电图研究中发现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.