Despite significant interest in the neural underpinnings of behavioral variability, little light has been shed on the cortical mechanism underlying the failure to respond to perceptual-level stimuli. We hypothesized that cortical activity resulting from perceptual-level stimuli is sensitive to the moment-to-moment fluctuations in cortical excitability, and thus may not suffice to produce a behavioral response. We tested this hypothesis using electrocorticographic recordings to follow the propagation of cortical activity in six human subjects that responded to perceptual-level auditory stimuli. Here we show that for presentations that did not result in a behavioral response, the likelihood of cortical activity decreased from auditory cortex to motor cortex, and was related to reduced local cortical excitability. Cortical excitability was quantified using instantaneous voltage during a short window prior to cortical activity onset. Therefore, when humans are presented with an auditory stimulus close to perceptual-level threshold, moment-by-moment fluctuations in cortical excitability determine whether cortical responses to sensory stimulation successfully connect auditory input to a resultant behavioral response.

尽管人们对行为变异性的神经基础有着浓厚的兴趣，但对于无法对感知水平刺激做出反应的皮层机制却知之甚少。我们假设由感知水平刺激引起的皮层活动对皮层兴奋性的瞬间波动敏感，因此可能不足以产生行为反应。我们使用皮层电图记录来测试这一假设，以跟踪对感知水平听觉刺激作出反应的六名人类受试者的皮层活动的传播。在这里，我们表明，对于没有导致行为反应的演示文稿，皮层活动的可能性从听觉皮层下降到运动皮层，并且与局部皮层兴奋性降低有关。在皮层活动开始前的一个短窗口期间，使用瞬时电压对皮层兴奋性进行量化。因此，当人类受到接近感知水平阈值的听觉刺激时，皮质兴奋性的每时每刻波动决定了皮质对感觉刺激的反应是否成功地将听觉输入与由此产生的行为反应联系起来。