Transcranial electrical stimulation and the neural dynamics of consciousness

意识的神经关联(NCC)已经被认真研究了大约30年。知觉意识已经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是意识到该区域计算的内容的原因。我们需要的是一个证据，证明对特定大脑区域的神经振荡的调制会或不会影响由该区域计算的到达意识的内容的可能性。我建议在双眼闪光抑制、元对比掩蔽、特罗克斯勒消失和操纵曝光持续时间方面进行大脑电刺激实验。这种范式通过揭示当有意识地感知刺激时与没有意识到刺激时相比，存在什么神经活动，从而帮助识别NCC。例如，一项元对比掩蔽研究表明，当相同的掩蔽目标可见和不可见时，脑电振荡功率、(头皮)电极间相位同步和事件相关电位更大。我的实验室显示，大约在双眼竞争中有意识的感知发生变化的时候，大脑相关区域网络中伽马功率和区域间相位同步以及theta-伽马跨频率耦合增加。在一项关于特罗克斯勒从我的实验室消失的研究中，我们发现，当一个改变了对比度的外围环保持在感知中时，比它消失时，额顶相位同步和传递熵更大。我建议在意识变化的范例中，以不同的方式直接使用经颅电刺激(TES)来调节相关的振荡频率。TES已被证明通过增加兴奋性(如经颅直流电刺激、经颅随机噪声刺激)和直接驱动神经振荡(经颅交流刺激)间接地调节神经振荡。交叉频率Tacs已被用来证明空间工作记忆依赖于theta(6赫兹)和高伽马(80-100赫兹)振荡的同步。同样，我建议确定视觉刺激的有意识知觉对相关大脑网络中的信息流(相位同步和传输熵)的依赖性。我曾做过一个实验，在特洛克斯勒消失期间，我用阳极或阴极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EEG来调查这种行为差异是否伴随着早期EEG研究中确定的额顶区之间的锁相值和/或传递熵的变化。在其他研究中，我将使用高清晰度TAC来直接调节所涉及的振荡频率，以便做出更直接和更准确的因果推断。

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.