{"day":"31","has_accepted_license":"1","publisher":"Institute of Science and Technology Austria","file":[{"content_type":"application/pdf","date_created":"2024-07-31T18:37:19Z","date_updated":"2025-01-31T23:30:03Z","embargo":"2025-01-31","creator":"lbollman","file_name":"PhD_Thesis_Lars_Bollmann.pdf","file_id":"17359","checksum":"12c76297cc27449da80c60d79127770d","access_level":"open_access","file_size":12920169,"relation":"main_file"},{"relation":"source_file","creator":"lbollman","file_name":"Latex_source.zip","embargo_to":"open_access","checksum":"19a0265079dec8038830ad6e35c5106e","file_id":"17360","access_level":"closed","file_size":27568807,"content_type":"application/zip","date_created":"2024-07-31T18:38:39Z","date_updated":"2025-01-31T23:30:03Z"}],"status":"public","degree_awarded":"PhD","citation":{"ista":"Bollmann L. 2024. Stability and change in the memory system during rest. Institute of Science and Technology Austria.","apa":"Bollmann, L. (2024). <i>Stability and change in the memory system during rest</i>. Institute of Science and Technology Austria. <a href=\"https://doi.org/10.15479/at:ista:17346\">https://doi.org/10.15479/at:ista:17346</a>","ama":"Bollmann L. Stability and change in the memory system during rest. 2024. doi:<a href=\"https://doi.org/10.15479/at:ista:17346\">10.15479/at:ista:17346</a>","ieee":"L. Bollmann, “Stability and change in the memory system during rest,” Institute of Science and Technology Austria, 2024.","chicago":"Bollmann, Lars. “Stability and Change in the Memory System during Rest.” Institute of Science and Technology Austria, 2024. <a href=\"https://doi.org/10.15479/at:ista:17346\">https://doi.org/10.15479/at:ista:17346</a>.","short":"L. Bollmann, Stability and Change in the Memory System during Rest, Institute of Science and Technology Austria, 2024.","mla":"Bollmann, Lars. <i>Stability and Change in the Memory System during Rest</i>. Institute of Science and Technology Austria, 2024, doi:<a href=\"https://doi.org/10.15479/at:ista:17346\">10.15479/at:ista:17346</a>."},"user_id":"ba8df636-2132-11f1-aed0-ed93e2281fdd","department":[{"_id":"GradSch"},{"_id":"JoCs"}],"month":"07","author":[{"first_name":"Lars","last_name":"Bollmann","id":"47AD3038-F248-11E8-B48F-1D18A9856A87","full_name":"Bollmann, Lars"}],"file_date_updated":"2025-01-31T23:30:03Z","oa_version":"Published Version","year":"2024","supervisor":[{"full_name":"Csicsvari, Jozsef L","id":"3FA14672-F248-11E8-B48F-1D18A9856A87","last_name":"Csicsvari","orcid":"0000-0002-5193-4036","first_name":"Jozsef L"}],"abstract":[{"lang":"eng","text":"Acquiring, retaining, and retrieving information over a wide range of timescales are crucial\r\nfunctions of the brain. The successful processing of memories affects many aspects of our\r\nlives and enables us and many other organisms to operate in a complex environment and\r\nto interact with it. In this context, the hippocampus and functionally connected brain\r\nareas, such as the prefrontal cortex, are central and have been subject to intensive research\r\nin the past decades. Storage of memories is believed to rely on distributed neural activity\r\nwithin these neural circuits. Additionally, neural memory traces of recent experience are\r\nreinstated during periods of rest or sleep. These reactivations are thought to play an\r\noutstanding role in the consolidation of memories and potentially facilitate the transfer of\r\ninformation from the hippocampus to cortical areas for long-term storage and integration\r\ninto existing knowledge.\r\nHowever, there is growing evidence that memory-related neural representations in the\r\nhippocampus are not as stable as initially thought and that they change even in the\r\nabsence of learning. It has been suggested that these changes reflect the accumulation of\r\nexperience, but the influence of interspersed consolidation periods has not been considered.\r\nPrevious studies have analyzed consolidation periods by detecting activity that strongly\r\nresembled neural activity during the acquisition of memory. Besides being often limited\r\nto only non-rapid eye movement (NREM) sleep, the used approaches were not capable of\r\ntracking changes in neural representations over extended temporal periods. More fluid\r\nrepresentations do not only challenge our understanding of how information is stored, but\r\nthey also affect the transfer of information between brain areas during the consolidation\r\nprocess.\r\nFor this thesis, I investigated the evolution of memory-related activity during sleep\r\nperiods expected to be involved in consolidation in the hippocampus and between the\r\nhippocampus and prefrontal cortex. I found that reactivated activity in the hippocampus\r\ngradually transformed during prolonged periods of sleep and inactivity. In the beginning,\r\nneural activity strongly resembled acquisition activity, whereas, with the progression of\r\ntime, it became more similar to the subsequent recall activity. NREM periods drove\r\nthis process, while rapid-eye movement (REM) periods showed a resetting effect. This\r\nreactivation drift was due to firing rate changes of a subset of cells and mirrored the\r\nrepresentational changes from the acquisition to the recall. A stable subset of cells\r\nwithstood the drift and maintained their activity. Therefore, my results indicate that\r\nmemory-related representations undergo spontaneous modifications during consolidation\r\nperiods and that these changes are predictive of representational drift.\r\nFurthermore, I found that the amount of change in the neural activity during subsequent\r\nsleep periods was biased by prior behavioral performance. Observed changes in the\r\nhippocampus and the prefrontal cortex were synchronized and increased after poor\r\nperformance, highlighting a potential role in the exchange of information. Low-variance\r\nvii\r\nperiods with distinct, more stable activity from a subset of cells significantly contributed\r\nto the heightened synchrony between both areas. Hence, interleaved phases of more stable\r\nneural activity could facilitate the information transfer between brain areas.\r\nIn conclusion, my investigations underline the fluidity of memory-related representations\r\nand assign a prominent role to sleep reactivation periods in their evolution. In addition, I\r\nidentified a potential mechanism of stable activity phases that might facilitate the synchronization across hippocampal-prefrontal activity despite ongoing changes. Reconciling\r\nand integrating findings from both spontaneous and behaviorally-related representational\r\nchanges in functionally related brain areas will help to broaden our understanding of how\r\nknowledge is stored, maintained, updated, and transferred between brain areas."}],"date_published":"2024-07-31T00:00:00Z","title":"Stability and change in the memory system during rest","date_updated":"2026-04-07T13:21:20Z","doi":"10.15479/at:ista:17346","publication_identifier":{"issn":["2663-337X"]},"language":[{"iso":"eng"}],"OA_place":"publisher","publication_status":"published","alternative_title":["ISTA Thesis"],"oa":1,"keyword":["Memory","Hippocampus","Consolidation"],"_id":"17346","ddc":["573"],"article_processing_charge":"No","type":"dissertation","date_created":"2024-07-29T15:08:42Z","page":"103","corr_author":"1"}