Zhao Xiaojie, Li Xiaoyun, Yao Li
College of Information Science and Technology, Beijing Normal University, Beijing, China.
Front Behav Neurosci. 2017 Oct 31;11:215. doi: 10.3389/fnbeh.2017.00215. eCollection 2017.
Working memory (WM) is a resource-limited memory system for temporary storage and processing of brain information during the execution of cognitive tasks. Increased WM load will increase the amount and difficulty of memory information. Several studies have used electroencephalography (EEG) or functional magnetic resonance imaging (fMRI) to explore load-dependent cognition processing according to the time courses of electrophysiological activity or the spatial pattern of blood oxygen metabolic activity. However, the relationships between these two activities and the underlying neural mechanism are still unclear. In this study, using simultaneously collected EEG and fMRI data under an n-back verbal WM task, we modeled the spectral perturbation of EEG oscillation and fMRI activation through joint independent component analysis (JICA). Multi-channel oscillation features were also introduced into the JICA model for further analysis. The results showed that time-locked activity of theta and beta were modulated by memory load in the early stimuli evaluation stage, corresponding to the enhanced activation in the frontal and parietal lobe, which were involved in stimulus discrimination, information encoding and delay-period activity. In the late response selection stage, alpha and gamma activity changes dependent on the load correspond to enhanced activation in the areas of frontal, temporal and parietal lobes, which played important roles in attention, information extraction and memory retention. These findings suggest that the increases in memory load not only affect the intensity and time course of the EEG activities, but also lead to the enhanced activation of brain regions which plays different roles during different time periods of cognitive process of WM.
工作记忆（WM）是一种资源有限的记忆系统，用于在执行认知任务期间临时存储和处理大脑信息。工作记忆负荷的增加会增加记忆信息的数量和难度。几项研究已经使用脑电图（EEG）或功能磁共振成像（fMRI），根据电生理活动的时间进程或血氧代谢活动的空间模式来探索负荷依赖性认知加工。然而，这两种活动之间的关系以及潜在的神经机制仍不清楚。在本研究中，我们在n-back言语工作记忆任务下同时收集EEG和fMRI数据，通过联合独立成分分析（JICA）对EEG振荡的频谱扰动和fMRI激活进行建模。多通道振荡特征也被引入JICA模型进行进一步分析。结果表明，在早期刺激评估阶段，θ波和β波的锁时活动受记忆负荷调制，对应于额叶和顶叶激活增强，这些脑区参与刺激辨别、信息编码和延迟期活动。在后期反应选择阶段，α波和γ波活动的变化取决于负荷，对应于额叶、颞叶和顶叶区域激活增强，这些脑区在注意、信息提取和记忆保持中起重要作用。这些发现表明，记忆负荷的增加不仅影响EEG活动的强度和时间进程，还会导致在工作记忆认知过程的不同时间段发挥不同作用的脑区激活增强。
