Sleep is critical for cognitive processing, learning, and memory stabilization. However, what happens during sleep is far more organized and dynamic than once believed. Recent research has shown that REM sleep involves patterns of neural communication seen during wakefulness. Two studies contribute important insights into the active nature of REM state. One demonstrates that lucid dreamers can perceive, evaluate, and respond to external information in real time, revealing that cognition remains accessible during REM. The other identifies a newly discovered fast neural oscillation that structures interhemispheric communication during both REM sleep and active behavior. Together, these show that REM sleep is a dynamic hybrid state. The mind remains partially open to the outside world while simultaneously engaging in complex internal coordination.
Dr. Torres Platas talked about “Real-time dialogue between experimenters and dreamers during REM sleep” (Konkoly et al., 2021). Konkoly and her colleagues provide striking evidence that dreamers can meaningfully communicate from within REM sleep. Their study examined lucid dreamers during REM sleep and if they were able to engage with external sensory signals presented by experimenters. These participants perceived questions, integrated them into the dream narrative, and then responded using predefined eye-movement or facial-muscle signals. Many were even able to solve novel math problems while dreaming, demonstrating their preserved access to working memory and reasoning. This suggests that REM sleep does not fully disconnect the brain from the environment but instead allows selective permeability, enabling the sleeper to process external cues while maintaining the immersive experience of the dream. These findings challenge traditional assumptions about the inaccessibility of the dreaming mind and provide a new method for probing dream cognition in real time.
While Konkoly et al. highlight the brain’s ability to process and respond to external information during REM, Ghosh and colleagues reveal the remarkable structure of internal neural communication occurring during this same sleep stage in “Running speed and REM sleep control two distinct modes of rapid interhemispheric communication.” Their research identifies a form of high-frequency oscillation, termed “splines,” in the retrosplenial cortex. These oscillations, occurring at 110-160 Hz, are most prominent in the granular retrosplenial cortex and are tightly phase-locked to ongoing theta rhythms. Splines exhibit anti-phase synchrony between the left and right hemispheres, suggesting cross-hemispheric communication different from gamma oscillations, which remain in-phase. Spline-rich periods coincide with heightened firing in both excitatory and inhibitory neurons across the retrosplenial cortex and hippocampus, indicating that these rhythms represent high-activity microstates embedded within REM sleep. Rather than being in a state of neural disconnection, REM appears to contain coordinated and energetically rich episodes that may contribute to spatial memory processing, dream imagery, or the integration of internally generated information.
Together, these studies depict REM sleep as a complex state that combines internal rhythmic coordination with preserved cognitive capacities. The demonstration of real-time communication from within lucid dreams indicates that the dreaming brain can access memory, evaluate sensory input, and general intentional responses. At the same time, discovery of splines show that REM is structured by interhemispheric rhythms that may organize the very content of dreams or support memory-related computations. These results change the long-held view that REM sleep is disconnected from the external world and emphasize that it is both internally dynamic and externally receptive.
These insights have broad implications for understanding memory processing, dream research, and the nature of consciousness. Fast oscillatory activity may scaffold the integration of memory traces during REM, while the cognitive continuity demonstrated in lucid dreamers highlights the persistence of reasoning and volition within the dream state. By revealing both the internal and external channels of communication available during REM sleep, the work done by Konkoly and Ghosh provides a deeper appreciation of the active, richly coordinated nature of the dreaming brain.
References
Ghosh, M., Yang, F.-C., Rice, S. P., Hetrick, V., Gonzalez, A. L., Siu, D., Brennan, E. K. W., John, T. T., Ahrens, A. M., & Ahmed, O. J. (2022). Running speed and REM sleep control two distinct modes of rapid interhemispheric communication. Cell Reports, 40(1), 111028. https://doi.org/10.1016/j.celrep.2022.111028
Konkoly, K. R., Appel, K., Chabani, E., Mangiaruga, A., Gott, J., Mallett, R., Caughran, B., Witkowski, S., Whitmore, N. W., Mazurek, C. Y., Berent, J. B., Weber, F. D., Türker, B., Leu-Semenescu, S., Maranci, J.-B., Pipa, G., Arnulf, I., Oudiette, D., Dresler, M., & Paller, K. A. (2021). Real-time dialogue between experimenters and dreamers during REM sleep. Current Biology, 0(0). https://doi.org/10.1016/j.cub.2021.01.026
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