The role of pre-stimulus oscillatory activity in predictive perception

Alpha oscillations (8–14 Hz) are the dominant rhythm in the awake brain, which is proposed to set the internal state of the neural system. Previous work has demonstrated that states of decreased spontaneous alpha oscillatory power correlate with enhanced neural excitability. However, whether and how changes in neural excitability influence sensory processing and manifest in behavior are yet open questions. To address these questions, we used a novel paradigm to experimentally manipulate human participants’ decision criterion (i.e., how certain percepts are used for decision) in a visual detection task. In different blocks, we primed participants differently with clearly visible stimuli to introduce either a liberal or conservative decision criterion for the subsequently presented ambiguous stimuli. While we observed prevalent criterion shifts in participants’ decisions under different priming conditions, the pre-stimulus oscillatory power or phase were not modulated by different priming conditions. Trial-by-trial analyses showed that lower spontaneous alpha oscillatory power in visual areas encoding the target stimuli leads to higher accuracy in performing the task, which is accompanied with enhanced information content decodable in the neural activity patterns. Moreover, spontaneous alpha oscillatory phase in anterior frontal and superior parietal regions modulate accuracy in a phasic sinusoidal manner. Together, our results indicate that as neural excitability increases in the state of decreased occipital alpha-band oscillatory power, the sensory representation of task-relevant visual stimuli is sharpened and consequently leads to improved behavioral discriminability.

α振荡（Alpha oscillations）是清醒大脑中的主导节律，被认为可调控神经系统的内部状态。既往研究证实，自发性α振荡功率降低的神经状态与神经兴奋性增强呈正相关。然而，神经兴奋性的变化是否以及如何影响感觉加工并在行为层面有所体现，仍是尚未解决的开放问题。为解答上述问题，我们在视觉检测任务中采用全新实验范式，对人类被试的决策标准（即感知信息用于决策的置信程度）进行实验性操控。在不同实验区块中，我们通过清晰可见的刺激对被试实施差异化启动操作，为后续呈现的模糊刺激分别设定宽松或保守的决策标准。尽管我们观察到不同启动条件下被试的决策普遍出现了标准偏移，但不同启动条件并未对刺激前的振荡功率或相位产生调控效应。逐试分析结果显示，编码目标刺激的视觉脑区内，自发性α振荡功率越低，任务执行准确率越高，同时神经活动模式中可解码的信息含量也随之提升。此外，前额叶前部与顶叶上部区域的自发性α振荡相位，以时相性正弦波动的方式调控任务准确率。综上，本研究结果表明：当枕叶α波段振荡功率降低、神经兴奋性增强时，任务相关视觉刺激的感觉表征会得到锐化，进而提升行为辨别能力。