Brüers Sasskia, VanRullen Rufin
UMR 5549, Faculté de Médecine Purpan, Centre National de la Recherche Scientifique, Toulouse, France.
Centre de Recherche Cerveau et Cognition, Université de Toulouse, Université Paul Sabatier, Toulouse, France.
Front Neurosci. 2018 Apr 25;12:279. doi: 10.3389/fnins.2018.00279. eCollection 2018.
Oscillations are ubiquitous in the brain. Alpha oscillations in particular have been proposed to play an important role in sensory perception. Past studies have shown that the power of ongoing EEG oscillations in the alpha band is negatively correlated with visual outcome. Moreover, it also co-varies with other endogenous factors such as attention, vigilance, or alertness. In turn, these endogenous factors influence visual perception. Therefore, it remains unclear how much of the relation between alpha and perception is indirectly mediated by such endogenous factors, and how much reflects a direct causal influence of alpha rhythms on sensory neural processing. We propose to disentangle the direct from the indirect causal routes by introducing modulations of alpha power, independently of any fluctuations in endogenous factors. To this end, we use white-noise sequences to constrain the brain activity of 20 participants. The cross-correlation between the white-noise sequences and the concurrently recorded EEG reveals the impulse response function (IRF), a model of the systematic relationship between stimulation and brain response. These IRFs are then used to reconstruct rather than record the brain activity linked with new random sequences (by convolution). Interestingly, this reconstructed EEG only contains information about oscillations directly linked to the white-noise stimulation; fluctuations in attention and other endogenous factors may still modulate brain alpha rhythms during the task, but our reconstructed EEG is immune to these factors. We found that the detection of near-perceptual threshold targets embedded within these new white-noise sequences depended on the power of the ~10 Hz reconstructed EEG over parieto-occipital channels. Around the time of presentation, higher power led to poorer performance. Thus, fluctuations in alpha power, induced here by random luminance sequences, can directly influence perception: the relation between alpha power and perception is not a mere consequence of fluctuations in endogenous factors.
振荡在大脑中无处不在。特别是阿尔法振荡被认为在感官知觉中起着重要作用。过去的研究表明，脑电图（EEG）在阿尔法波段的持续振荡功率与视觉结果呈负相关。此外，它还与其他内源性因素共同变化，如注意力、警觉性或机敏度。反过来，这些内源性因素会影响视觉感知。因此，目前尚不清楚阿尔法与感知之间的关系有多少是由这些内源性因素间接介导的，又有多少反映了阿尔法节律对感觉神经处理的直接因果影响。我们建议通过引入阿尔法功率调制来区分直接因果路径和间接因果路径，而不考虑内源性因素的任何波动。为此，我们使用白噪声序列来约束20名参与者的大脑活动。白噪声序列与同时记录的脑电图之间的互相关揭示了脉冲响应函数（IRF），它是刺激与大脑反应之间系统关系的模型。然后，这些IRF被用于重建而非记录与新随机序列相关的大脑活动（通过卷积）。有趣的是，这种重建的脑电图只包含与白噪声刺激直接相关的振荡信息；在任务过程中，注意力和其他内源性因素的波动可能仍会调节大脑阿尔法节律，但我们重建的脑电图不受这些因素影响。我们发现，检测嵌入在这些新白噪声序列中的接近感知阈值的目标，取决于顶枕通道上约10Hz重建脑电图的功率。在呈现目标时，较高的功率会导致较差的表现。因此，由随机亮度序列诱发的阿尔法功率波动可以直接影响感知：阿尔法功率与感知之间的关系不仅仅是内源性因素波动的结果。
