Probing the interaction of bottom-up and top-down processing in bistable perception: on the causal role of brain oscillations

了解可逆图形的双稳态背后的神经机制可能会为我们的视觉系统的正常运作提供有价值的见解。控制可逆图形知觉变化的因素可分为自下而上的感觉过程(如适应)和认知自上而下的过程(如注意)。目前关于模棱两可的数字的理论主张采用混合方法，这种方法认为双稳态认知源于自下而上和自上而下的过程之间的相互作用。然而，来自经验神经科学的直接证据仍然缺乏这种相互作用。在这里，我们建议将脑振荡作为一种候选机制，它能够反映广泛分布的皮质网络中的局部自下而上过程和更多的全球大规模相互作用。更具体地说，我们的目标是测试这一模型，即前部伽马频段活动反映了注意的自上而下的过程，而后部的阿尔法活动反映了破坏当前感知的适应性的自下而上的过程。为了确定伽马和阿尔法振荡在双稳态知觉中的因果作用，我们利用了一种新的非侵入性人脑刺激技术--经颅交流电刺激(TACS)，它通过将振荡电流施加到人类头皮来直接调节正在进行的有节奏的大脑活动。并行的TAC和EEG记录可以分析伽马和阿尔法频率的相互关系及其对图形反转的影响。

Understanding the neural mechanisms underlying the bistability of reversible figures may provide valuable insights into the normal functioning of our visual system. The proposed factors that control the perceptual alternations of reversible figures can be classified into sensory bottom-up processes like adaptation and cognitive top-down processes like attention. Current theories of ambiguous figures argue for hybrid approaches, which conceive bistable perception as arising from interactions between bottom-up and top-down processes. However, direct evidence from empirical neuroscience for such an interaction is still lacking. Here, we propose brain oscillations as a candidate mechanism that is capable of reflecting both local bottom-up processes and more global large-scale interactions within widely distributed cortical networks. More specifically, we aim to test the model that frontal gamma band activity reflects attentional top-down processes, whereas posterior alpha activity reflects adaptation-like bottom-up processes that destabilize the current percept. To establish a causal role for gamma and alpha oscillations in bistable perception, we capitalize on a new technique of noninvasive human brain stimulation, transcranial alternating current stimulation (tACS), which directly modulates the ongoing rhythmic brain activity by the application of oscillatory currents to the human scalp. Parallel tACS and EEG recordings allow for analyzing the interrelation of gamma and alpha frequencies and their impact on figure reversal.