Studies of memory reactivation during sleep using intracranial recordings

The ability to remember is central to human success. This ability requires registering new information adequately so that it can be retrieved at a later time. Yet, here we emphasize that the ability to remember also depends on intervening practice. In particular, memory success may depend on memory reactivation during sleep, which changes memory storage. In prior work, prompting reactivation of specific memories during sleep selectively improved recall, but we have much to learn about the neurocognitive basis of this processing. This project makes use of two special populations to shed new light on how sleep can help reduce forgetting. First, in patients with epilepsy we examine intracranial electroencephalographic recordings from specific anatomical locations such as the hippocampus, where neural replay can be found. Second, in people with Highly Superior Autobiographical Memory (HSAM), we ask whether memory processing during sleep contributes to superior abilities. An overarching objective is to specify features of memory processing during sleep that help memories remain available for later remembering. To make progress at this intriguing intersection of memory research and sleep research, we will study memory processing in two special populations, patients with implanted electrodes and individuals with outstanding recall. In our prior work, we developed methods for using direct manipulations during sleep to advance understanding of sleep-based memory consolidation. The key intellectual merit of this project is to expand knowledge of sleep physiology relevant to memory consolidation in humans. One way to do that is to obtain recordings from the human hippocampus, which are only possible in rare circumstances. This brain region is already known to be relevant for replay from studies of place cells in rodents, but there is great difficulty translating that work to human memory abilities. By investigating human hippocampal responses that implicate memory replay and consolidation, we will make strides in linking the rodent research to human memory function. and we will acquire new knowledge about the physiology of beneficial memory processing during sleep. We will study memory phenomena typical of what humans need to remember in daily life outside the laboratory. Advanced analyses of hippocampal and cortical activity will provide new information about neural processing that contributes to memory consolidation. We will thus learn more, in particular, about how hippocampal memory reactivation during sleep helps to make later memory retrieval accurate. Highly accurate remembering is the defining feature of HSAM, but the remarkable abilities these people exhibit are largely unexplained. We will endeavor to substantiate our pilot results showing that sleep physiology in HSAM is unusual in the high frequency of sleep spindles, converging with other results suggesting that critical memory processing happens when sleep spindles are generated in thalamocortical networks. This research delves into complex memory mechanisms while also providing cognitive neuroscience training opportunities for trainees at all levels, including scientists from underrepresented groups. Findings will be disseminated widely, both in the scientific literature and for the general public, and will lead to insights into memory function that will enhance public understanding and appreciation of science. The broader relevance of our work will enable connections among investigations of detailed physiology in rodents, memory processing in humans, and extraordinary memory. O