CNRS, UMR5549, Centre de Recherche Cerveau et Cognition, Faculté de Médecine de Purpan, 31062 Toulouse, France.
J Neurosci. 2011 Aug 17;31(33):11889-93. doi: 10.1523/JNEUROSCI.1161-11.2011.
Why does neuronal activity in sensory brain areas sometimes give rise to perception, and sometimes not? Although neuronal noise is often invoked as the key factor, a portion of this variability could also be due to the history and current state of the brain affecting cortical excitability. Here we directly test this idea by examining whether the phase of prestimulus oscillatory activity is causally linked with modulations of cortical excitability and with visual perception. Transcranial magnetic stimulation (TMS) was applied over human visual cortex to induce illusory perceptions (phosphenes) while electroencephalograms (EEGs) were simultaneously recorded. Subjects reported the presence or absence of an induced phosphene following a single pulse of TMS at perceptual threshold. The phase of ongoing alpha (∼10 Hz) oscillations within 400 ms before the pulse significantly covaried with the perceptual outcome. This effect was observed in occipital regions around the site of TMS, as well as in a distant frontocentral region. In both regions, we found a systematic relationship between prepulse EEG phase and perceptual performance: phosphene probability changed by ∼15% between opposite phases. In summary, we provide direct evidence for a chain of causal relations between the phase of ongoing oscillations, neuronal excitability, and visual perception: ongoing oscillations create periodic "windows of excitability," with sensory perception being more likely to occur at specific phases.
为什么感觉脑区的神经元活动有时会引起感知，而有时却不会？虽然神经元噪声通常被认为是关键因素，但这种可变性的一部分也可能是由于大脑的历史和当前状态影响皮质兴奋性。在这里，我们通过直接检查刺激前振荡活动的相位是否与皮质兴奋性的调制以及视觉感知有关，来检验这个想法。我们在人类视觉皮层上应用经颅磁刺激（TMS）以诱导幻觉（闪光），同时记录脑电图（EEG）。在 TMS 达到感知阈值后，受试者报告单个脉冲后是否出现诱导的闪光。脉冲前 400 毫秒内的持续 alpha（~10 Hz）振荡的相位与感知结果显著相关。这种效应在 TMS 部位周围的枕部区域以及远处的额-中央区域都观察到。在这两个区域，我们都发现了 prepulse EEG 相位和感知性能之间的系统关系：在相反相位之间，闪光概率变化了约 15%。总之，我们为持续振荡的相位、神经元兴奋性和视觉感知之间的因果关系链提供了直接证据：持续的振荡产生周期性的“兴奋性窗口”，在特定相位下更有可能发生感官感知。
