University of Florida, Gainesville, FL 32611, USA.
J Cogn Neurosci. 2011 Jun;23(6):1379-94. doi: 10.1162/jocn.2010.21478. Epub 2010 May 11.
Understanding the relation between prestimulus neural activity and subsequent stimulus processing has become an area of active investigation. Computational modeling, as well as in vitro and in vivo single-unit recordings in animal preparations, have explored mechanisms by which background synaptic activity can influence the responsiveness of cortical neurons to afferent input. How these mechanisms manifest in humans is not well understood. Although numerous EEG/MEG studies have considered the role of prestimulus alpha oscillations in the genesis of visual-evoked potentials, no consensus has emerged, and divergent reports continue to appear. The present work addresses this problem in three stages. First, a theoretical model was developed in which the background synaptic activity and the firing rate of a neural ensemble are related through a sigmoidal function. The derivative of this function, referred to as local gain, has an inverted-U shape and is postulated to be proportional to the trial-by-trial response evoked by a transient stimulus. Second, the theoretical model was extended to noninvasive studies of human visual processing, where the model variables are reinterpreted in terms of ongoing EEG oscillations and event-related potentials. Predictions were derived from the model and tested by recording high-density scalp EEG from healthy volunteers performing a trial-by-trial cued spatial visual attention task. Finally, enhanced stimulus processing by attention was linked to an increase in the overall slope of the sigmoidal function. The commonly observed reduction of alpha magnitude with attention was interpreted as signaling a shift of the underlying neural ensemble toward an optimal excitability state that enables the increase in global gain.
理解刺激前神经活动与随后的刺激处理之间的关系已经成为一个活跃的研究领域。计算建模以及动物实验中的体外和体内单细胞记录已经探索了背景突触活动如何影响皮质神经元对传入输入的反应性的机制。这些机制在人类中是如何表现的还不是很清楚。尽管许多 EEG/MEG 研究都考虑了刺激前 alpha 振荡在视觉诱发电位产生中的作用，但尚未达成共识，并且仍在不断出现相互矛盾的报告。本研究分三个阶段解决了这个问题。首先，开发了一个理论模型，其中背景突触活动和神经集合的放电率通过一个 sigmoid 函数相关。该函数的导数，称为局部增益，呈倒 U 形，据推测与瞬态刺激引起的逐次反应成正比。其次，将理论模型扩展到人类视觉处理的非侵入性研究中，其中模型变量根据持续的 EEG 振荡和事件相关电位进行重新解释。从模型中得出预测，并通过记录健康志愿者执行逐次提示空间视觉注意力任务时的高密度头皮 EEG 进行测试。最后，注意力增强的刺激处理与 sigmoid 函数整体斜率的增加有关。通常观察到的注意力增加时 alpha 幅度减小被解释为信号表明基础神经集合向最佳兴奋性状态转移，从而增加全局增益。
