Institute of Neuroscience and Psychology, University of Glasgow, Glasgow G12 8QB, UK,
Institute of Neuroscience and Psychology, University of Glasgow, Glasgow G12 8QB, UK.
J Neurosci. 2019 Apr 17;39(16):3119-3129. doi: 10.1523/JNEUROSCI.1633-18.2019. Epub 2019 Feb 15.
Two largely independent research lines use rhythmic sensory stimulation to study visual processing. Despite the use of strikingly similar experimental paradigms, they differ crucially in their notion of the stimulus-driven periodic brain responses: one regards them mostly as synchronized (entrained) intrinsic brain rhythms; the other assumes they are predominantly evoked responses [classically termed steady-state responses (SSRs)] that add to the ongoing brain activity. This conceptual difference can produce contradictory predictions about, and interpretations of, experimental outcomes. The effect of spatial attention on brain rhythms in the alpha band (8-13 Hz) is one such instance: alpha-range SSRs have typically been found to increase in power when participants focus their spatial attention on laterally presented stimuli, in line with a gain control of the visual evoked response. In nearly identical experiments, retinotopic decreases in entrained alpha-band power have been reported, in line with the inhibitory function of intrinsic alpha. Here we reconcile these contradictory findings by showing that they result from a small but far-reaching difference between two common approaches to EEG spectral decomposition. In a new analysis of previously published human EEG data, recorded during bilateral rhythmic visual stimulation, we find the typical SSR gain effect when emphasizing stimulus-locked neural activity and the typical retinotopic alpha suppression when focusing on ongoing rhythms. These opposite but parallel effects suggest that spatial attention may bias the neural processing of dynamic visual stimulation via two complementary neural mechanisms. Attending to a visual stimulus strengthens its representation in visual cortex and leads to a retinotopic suppression of spontaneous alpha rhythms. To further investigate this process, researchers often attempt to phase lock, or entrain, alpha through rhythmic visual stimulation under the assumption that this entrained alpha retains the characteristics of spontaneous alpha. Instead, we show that the part of the brain response that is phase locked to the visual stimulation increased with attention (as do steady-state evoked potentials), while the typical suppression was only present in non-stimulus-locked alpha activity. The opposite signs of these effects suggest that attentional modulation of dynamic visual stimulation relies on two parallel cortical mechanisms-retinotopic alpha suppression and increased temporal tracking.
两条主要的独立研究路线都使用有节奏的感官刺激来研究视觉处理。尽管使用了惊人相似的实验范式，但它们在刺激驱动的周期性大脑反应的概念上存在关键差异：一种观点认为这些反应主要是同步（锁定）的内在大脑节律；另一种观点则假设它们主要是诱发反应[经典称为稳态反应（SSRs）]，这些反应会叠加在正在进行的大脑活动上。这种概念差异可能会对实验结果产生矛盾的预测和解释。空间注意力对 alpha 频段（8-13Hz）脑节律的影响就是一个这样的例子：当参与者将空间注意力集中在侧向呈现的刺激上时，alpha 频段范围内的 SSR 通常会增加，这与视觉诱发反应的增益控制一致。在几乎完全相同的实验中，已经报道了与内在 alpha 的抑制功能一致的有节奏的 alpha 频段功率的视网膜下降。在这里，我们通过显示它们是由两种常见的 EEG 光谱分解方法之间的一个小但影响深远的差异引起的，从而调和了这些矛盾的发现。在对以前发表的人类 EEG 数据的新分析中，这些数据是在双侧有节奏的视觉刺激期间记录的，我们发现当强调与刺激锁定的神经活动时，会出现典型的 SSR 增益效应，而当专注于正在进行的节律时，会出现典型的视网膜 alpha 抑制。这些相反但平行的效应表明，空间注意力可能通过两种互补的神经机制来影响动态视觉刺激的神经处理。注意一个视觉刺激会增强其在视觉皮层中的表示，并导致自发 alpha 节律的视网膜抑制。为了进一步研究这个过程，研究人员通常试图通过有节奏的视觉刺激来使 alpha 同步锁相，或锁定，假设这种锁定的 alpha 保留了自发 alpha 的特征。相反，我们表明，与视觉刺激同步锁定的大脑反应部分随着注意力的增加而增加（如稳态诱发电位），而典型的抑制仅存在于非刺激锁定的 alpha 活动中。这些效应的相反符号表明，动态视觉刺激的注意力调节依赖于两种平行的皮质机制-视网膜 alpha 抑制和增强的时间跟踪。
