Working memory (WM) is a keystone of our cognitive abilities. Increasing load has been shown to dampen its performance and affect oscillatory neural activity in different frequency bands. Nevertheless, mixed results regarding fast frequencies activity and a lack of research on WM load modulations of cross-frequency phase-amplitude coupling mechanisms preclude a better understanding of the impact of increased WM load levels on brain activity as well as inter-regional communication and coordination supporting WM processes. Hence, we analyzed the EEG activity of 25 participants while performing a delayed-matching-to-sample (DMS) WM task with three WM load levels. Current density power and distribution at the source level for theta, beta, and gamma frequencies during the task's delay period were compared for each pair of WM load conditions. Results showed maximal increases of theta activity in frontal areas and of fast frequencies' activity in posterior regions with WM load, showing the involvement of frontal theta activity in WM maintenance and the control of attentional resources and visual processing by beta and gamma activity. To study whether WM load modulates communication between cortical areas, posterior beta and gamma amplitudes distribution across frontal theta phase was also analysed for those areas showing the largest significant WM load modulations. Higher beta activity amplitude at bilateral cuneus and right middle occipital gyrus, and higher gamma activity amplitude at bilateral posterior cingulate were observed during frontal theta phase peak in low than high memory load conditions. Moreover, greater fast beta amplitude at the right postcentral gyrus was observed during theta phase trough at right middle frontal gyrus in high than low memory load conditions. These results show that WM load modulates whether interregional communication occurs during theoretically optimal or non-optimal time windows, depending on the demands of frontal control of posterior areas required to perform the task successfully.

工作记忆 (WM) 是我们认知能力的基石。已显示增加负载会抑制其性能并影响不同频段的振荡神经活动。然而，关于快速频率活动的混合结果和缺乏对跨频率相位幅度耦合机制的 WM 负载调制的研究妨碍了更好地理解增加的 WM 负载水平对大脑活动以及区域间沟通和协调的影响支持 WM 流程。因此，我们在执行具有三个 WM 负载级别的延迟匹配样本 (DMS) WM 任务时分析了 25 名参与者的 EEG 活动。对于每对 WM 负载条件，比较了任务延迟期间的 theta、beta 和 gamma 频率在源级的电流密度功率和分布。结果显示，在 WM 负荷下，额叶区域的 theta 活动和后部区域的快频率活动最大增加，表明额叶 theta 活动参与了 WM 的维持以及通过 beta 和 gamma 活动控制注意力资源和视觉处理。为了研究 WM 负载是否调节皮质区域之间的通信，还分析了额叶 theta 相位的后 beta 和 gamma 振幅分布，以发现那些显示最大显着 WM 负载调制的区域。双侧楔叶和右侧枕中回的 β 活动幅度较高，而双侧后扣带回的 γ 活动幅度较高，在低记忆负荷条件下的额叶 theta 相位峰值期间观察到。而且，在高记忆负荷条件下，在右侧额中回的θ相波谷期间，在右侧中央后回观察到更大的快速β振幅。这些结果表明，WM 负载会调节区域间通信是否发生在理论上的最佳时间窗口或非最佳时间窗口，这取决于成功执行任务所需的后部区域的正面控制需求。