Recently, Professor Canhuang Luo from the School of Psychology, Shenzhen University, together with collaborators, published a research article in Proceedings of the National Academy of Sciences of the United States of America (PNAS, 2024 Impact Factor = 9.1), a prestigious journal indexed in the Nature Index. The paper, titled “Traveling waves link human visual and frontal cortex during working memory-guided behavior,” analyzed traveling-wave activity in human EEG data and revealed that, during memory-guided behavior, feedforward and feedback traveling waves occur between the visual and motor regions. These neural dynamics were found to effectively predict behavioral responses, suggesting that traveling waves may serve as an information transmission mechanism supporting the transformation of visual working memory into concrete actions. Professor Luo is the first author of the paper, with Shenzhen University as the first-affiliated institution. He and Professor Edward Ester from the University of Nevada, Reno, are co-corresponding authors.
Humans have the remarkable ability to formulate plans in their minds based on external information and internal needs, and then to act in a goal-directed manner. Such flexible, purposeful behavior relies heavily on working memory—the cognitive system responsible for temporarily storing and manipulating information. Working memory bridges immediate sensory input with upcoming actions, enabling individuals to act at the appropriate moment based on remembered information, rather than responding to the environment immediately. According to the sensory recruitment hypothesis, working memory relies on the same cortical regions responsible for sensory processing to maintain task-relevant information. However, for working memory to guide subsequent behavior, this sensory information must eventually be transformed into motor commands and transmitted to motor regions. How exactly this transformation and transmission occur has remained unclear—until now.
During working memory-guided behavior, the movement and propagation of neural oscillations may serve as the mechanism through which the visual and motor regions communicate. Neural oscillations refer to rhythmic neural activity in the brain that coordinates dynamic interactions across regions, enabling effective information exchange among neuronal populations. Within the cerebral cortex, such oscillatory activity can manifest as spatial propagation, a phenomenon known as traveling waves. Previous studies have shown that traveling waves are closely linked to perceptual and cognitive processes, and may play a crucial role in information transmission and integration across brain regions. Building on this foundation, the present study investigated whether communication between the visual and motor areas during working memory-guided behavior relies on cortical traveling waves.
To address this question, the researchers analyzed two publicly available datasets (Experiment 1 and Experiment 2). In the analysis of Experiment 1, they first examined whether traveling waves occurred between task-relevant brain regions during memory-guided responses. In this experiment, participants were required to memorize and later recall the orientation of a line presented either in the left or right visual field, and then respond with either their left or right hand (Fig. 1A). The pairing of stimulus location and response hand was fully randomized—for example, a left-field stimulus could be responded to with either the left or the right hand. This design allowed the researchers to dissociate task-relevant brain regions associated with stimulus location and response hand (i.e., contralateral regions), thereby enabling a targeted investigation of traveling-wave activity between these areas (Fig. 1B). Subsequently, the EEG signals recorded during the response phase were subjected to traveling-wave analysis. This method represents EEG data as a two-dimensional matrix, with electrodes on one axis and time on the other. By identifying spatiotemporal patterns within the matrix that exhibit clear directional structure, the analysis detects the presence of potential traveling-wave activity (Fig. 1C–F).
Figure 1. Experimental task and traveling-wave analysis pipeline。
The results showed that during the response phase, significant feedforward theta (2–6 Hz) traveling waves and feedback beta (14–32 Hz) traveling waves emerged across electrodes spanning task-relevant sensory and motor regions. The feedforward theta waves appeared just before response initiation, reaching peak strength at the onset of the response. Notably, their activity could reliably predict both the initiation time and the duration of participants’ responses (Fig. 2A–D). Following response completion, beta traveling waves propagating in the opposite direction were observed. The timing of these feedback beta waves was predictive of participants’ response termination (Fig. 2A, E).
Figure 2. Results of Experiment 1. Feedforward theta and feedback beta traveling waves between visual and motor electrodes, and their relationship to behavior
To further confirm whether these traveling waves were directly related to the execution of actions—rather than merely reflecting a preparatory task set—the researchers analyzed a second dataset (Experiment 2). In this task, participants were informed in advance about both the stimulus they would report and the hand they would use to respond, but were required to wait several seconds before making their response (Fig. 3A).
The results revealed that no feedforward theta or feedback beta traveling waves were observed during the waiting period (Fig. 3B). These traveling waves emerged only during the actual execution of the response (Fig. 3C). This finding demonstrates that the observed traveling waves are specifically associated with the process of action execution, rather than with action preparation.
Figure 3. Results of Experiment 2. Feedforward theta and feedback beta traveling waves appeared only during actual response execution
In summary, the dynamic propagation of feedforward theta and feedback beta traveling waves between sensory and motor regions not only predicted participants’ memory-guided behavioral responses, but also emerged exclusively during the actual execution of actions. These findings suggest that feedforward and feedback traveling waves serve as a critical bridge linking sensory memory with motor output in the generation of working memory-guided behavior.
This study provides a new perspective for understanding how working memory is transformed into concrete behavior, highlighting traveling waves as a potentially general mechanism for information transmission in the brain—playing a central role in sensory–motor integration and memory-driven behavior.
This research was supported by the Scientific Research Start-up Fund of Shenzhen University.
Original article link:
https://www.pnas.org/doi/10.1073/pnas.2415573122
