{"month":"01","type":"dissertation","status":"public","date_published":"2024-01-19T00:00:00Z","title":"Adaptive hierarchical representations in the hippocampus","citation":{"ieee":"H. S. C. Chiossi, “Adaptive hierarchical representations in the hippocampus,” Institute of Science and Technology Austria, 2024.","chicago":"Chiossi, Heloisa S. C. “Adaptive Hierarchical Representations in the Hippocampus.” Institute of Science and Technology Austria, 2024. <a href=\"https://doi.org/10.15479/at:ista:14821\">https://doi.org/10.15479/at:ista:14821</a>.","ama":"Chiossi HSC. Adaptive hierarchical representations in the hippocampus. 2024. doi:<a href=\"https://doi.org/10.15479/at:ista:14821\">10.15479/at:ista:14821</a>","apa":"Chiossi, H. S. C. (2024). <i>Adaptive hierarchical representations in the hippocampus</i>. Institute of Science and Technology Austria. <a href=\"https://doi.org/10.15479/at:ista:14821\">https://doi.org/10.15479/at:ista:14821</a>","ista":"Chiossi HSC. 2024. Adaptive hierarchical representations in the hippocampus. Institute of Science and Technology Austria.","mla":"Chiossi, Heloisa S. C. <i>Adaptive Hierarchical Representations in the Hippocampus</i>. Institute of Science and Technology Austria, 2024, doi:<a href=\"https://doi.org/10.15479/at:ista:14821\">10.15479/at:ista:14821</a>.","short":"H.S.C. Chiossi, Adaptive Hierarchical Representations in the Hippocampus, Institute of Science and Technology Austria, 2024."},"file_date_updated":"2025-01-19T23:30:04Z","date_updated":"2026-04-07T13:21:56Z","publication_identifier":{"issn":["2663-337X"]},"page":"89","year":"2024","department":[{"_id":"GradSch"},{"_id":"JoCs"}],"project":[{"_id":"2564DBCA-B435-11E9-9278-68D0E5697425","call_identifier":"H2020","grant_number":"665385","name":"International IST Doctoral Program"}],"publication_status":"published","abstract":[{"lang":"eng","text":"The hippocampus is central to memory formation, storage and retrieval over many\r\ntimescales. Neurons in this brain area are highly selective to spatial position as well as to many\r\nother variables of the environment. It is believed that the selectivity patterns of hippocampal\r\nneurons reflect the structure of tasks an animal performs. However, especially at timescales\r\nlonger than a few minutes or hours it is not fully known how these representations evolve, nor\r\nhow they map to behaviour in the process. In this thesis, I monitored the evolution of\r\nhippocampal representations in a novel spatial-associative memory task for rats. Reward\r\nlocations were associated with global sensory cues (i.e. context); animals had to remember the\r\nassociations and dig for food in those locations only. I used in vivo electrophysiology to record\r\nthe activity of the hippocampus dorsal CA1 neurons during the learning period of a few days.\r\nI report here a novel and simple method to classify behaviour performance to account\r\nfor individual variability in learning speed and spurious performance unrelated to true task rule\r\nlearning. Using this classification I was then able to investigate neural responses on different\r\nstages of learning matched across animals. On the first day of learning, I observed a fast\r\nformation of single-cell selectivity to task variables which remained stable over days. I also\r\nobserved that reward tuning was not a single process but dependent on task-related cognitive\r\nload. At the population level, a linear decoding approach revealed a hierarchy in the\r\nrepresentation of task variables that changed with learning. In the high-dimensional space of\r\npopulation activity, the representation of contexts was specific to each position in the maze, and\r\ncould thus be better decoded if the position was known. The decoding of position did not improve\r\nwith knowledge of other variables. As learning progressed, the hippocampal code underwent a\r\nreorganisation of high-variance directions in population activity, identified by principal\r\ncomponent analysis. I found that dominant dimensions started carrying increasing amounts of\r\ninformation about task context specifically at those positions where it mattered for task\r\nperformance. When I contrasted this with variables less relevant to task performance (e.g.\r\nmovement direction), I did not observe differences in decoding quality over positions nor a\r\nreduction of dimensionality with learning.\r\nOverall, the largest changes in CA1 neural response with task learning happened in a\r\nmatter of a few trials; over days, changes undetectable in single-cell statistics were responsible\r\nfor re-structuring the hierarchy of neural representations at the population level; these changes\r\nwere task-specific and reflected different stages of learning. This indicates that complex task\r\nlearning may involve different magnitudes of response modulation in CA1, which happen at\r\nspecific time scales linked to behaviour."}],"fulldoi":"https://doi.org/10.15479/at:ista:14821","doi":"10.15479/at:ista:14821","corr_author":"1","degree_awarded":"PhD","alternative_title":["ISTA Thesis"],"_id":"14821","publisher":"Institute of Science and Technology Austria","oa_version":"Published Version","article_processing_charge":"No","language":[{"iso":"eng"}],"day":"19","file":[{"file_id":"14838","content_type":"application/vnd.openxmlformats-officedocument.wordprocessingml.document","date_updated":"2025-01-19T23:30:04Z","relation":"source_file","file_name":"PhD_Thesis_190124.docx","date_created":"2024-01-19T11:04:05Z","checksum":"d3fa3de1abd5af5204c13e9d55375615","creator":"hchiossi","file_size":8656268,"access_level":"closed","embargo_to":"open_access"},{"date_updated":"2025-01-19T23:30:04Z","content_type":"application/pdf","file_id":"14839","file_name":"PhD_Thesis_190124.pdf","date_created":"2024-01-19T11:03:59Z","relation":"main_file","embargo":"2025-01-19","creator":"hchiossi","checksum":"13adc8dcfb5b6b18107f89f0a98fa8bd","access_level":"open_access","file_size":6567275}],"ddc":["570"],"supervisor":[{"id":"3FA14672-F248-11E8-B48F-1D18A9856A87","last_name":"Csicsvari","orcid":"0000-0002-5193-4036","first_name":"Jozsef L","full_name":"Csicsvari, Jozsef L"}],"OA_place":"publisher","user_id":"ba8df636-2132-11f1-aed0-ed93e2281fdd","author":[{"id":"2BBA502C-F248-11E8-B48F-1D18A9856A87","last_name":"Chiossi","orcid":"0009-0004-2973-278X","first_name":"Heloisa","full_name":"Chiossi, Heloisa"}],"ec_funded":1,"oa":1,"has_accepted_license":"1","date_created":"2024-01-16T14:25:21Z"}