One of the most compelling areas of neuroscience is how the brain processes information and forms memories during sleep, especially given how context-dependent memory formation can be. Before Dr. Torres-Platas’ deeply intriguing presentation about contemplative sleep practices, the study “Real-time dialogue between experimenters and dreamers during REM sleep,” by Konkoly et al., provides ample background with findings showing that during REM sleep, under the conditions of lucid dreaming, sleepers can actually engage in two-way communication. They can perceive external questions and respond in real time using volitional signals (like eye movements or facial-muscle contractions). This demonstrates that even during sleep, the brain can maintain complex cognitive functions. Their findings suggest that the sleeping brain isn’t simply disconnected from the rest of the world and its regular processing; rather, certain forms of conscious-like processing remain accessible. This allows for direct interrogation of dream-state cognition and perhaps even real-time memory activation during sleep. The work done in this study challenges older views that claimed that sleep was a purely passive state for memory consolidation. It also provides an interactive direction in which memories and ongoing cognition during sleep can be activated, manipulated, and even potentially modified. If memory traces (or engrams) remain at least partially accessible during REM sleep, then sleep may serve not only as a form of consolidation, but also for dynamic memory processing, or integration of new information.
More recent work done in 2023 by Abdellahi et al. in the study “Targeted memory reactivation in human REM sleep elicits detectable reactivation” builds on this by providing direct evidence that memories learned while awake can be reactivated during REM sleep. By using a targeted memory reactivation (TMR) paradigm, the researchers paired learned material during wakefulness with sound cues during wakefulness, and then replayed those cues during REM sleep. Through using EEG combined with machine-learning classifiers, they were able to detect brain activity patterns during REM sleep that strongly resembled the patterns seen during wakefulness, while performing the task. Most importantly and interestingly, the strength of this reactivation predicted participants’ performance improvements the next day. The work done in this study clearly shows that targeted memory cues during REM sleep can trigger memory reactivation patterns that closely resemble those seen while individuals are awake and performing the task.
Together, these studies work to significantly advance our understanding of the role and participation of memory during sleep. The Konkoly et al. findings show that, at least in some individuals, the sleeping brain remains functionally capable of processing and responding to stimuli. The work done by Abdellahi et al. then provides statistical evidence that specific memories encoded during wake can be restored during REM sleep. When looking at both studies side by side, it is evident that memories formed while a human is awake are not sealed off/inaccessible during sleep; instead, they stay accessible and can even be adjusted or reactivated. Overall, this supports a view of memory as a fluid and living process. A structure where encoding, retrieval, consolidation, and transformation can overlap across wake and sleep states, while being simultaneously influenced by both internal neural states and externally applied cues.
References
Abdellahi, M. E. A., Koopman, A. C. M., Treder, M. S., & Lewis, P. A. (2023). Targeted memory reactivation in human REM sleep elicits detectable reactivation. eLife, 12, e84324. https://doi.org/10.7554/eLife.84324
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, 31(7), 1417–1427.e6. https://doi.org/10.1016/j.cub.2021.01.026
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