---
OA_place: publisher
_id: '14821'
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."
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Heloisa
full_name: Chiossi, Heloisa
id: 2BBA502C-F248-11E8-B48F-1D18A9856A87
last_name: Chiossi
orcid: 0009-0004-2973-278X
citation:
ama: Chiossi HSC. Adaptive hierarchical representations in the hippocampus. 2024.
doi:10.15479/at:ista:14821
apa: Chiossi, H. S. C. (2024). Adaptive hierarchical representations in the hippocampus.
Institute of Science and Technology Austria. https://doi.org/10.15479/at:ista:14821
chicago: Chiossi, Heloisa S. C. “Adaptive Hierarchical Representations in the Hippocampus.”
Institute of Science and Technology Austria, 2024. https://doi.org/10.15479/at:ista:14821.
ieee: H. S. C. Chiossi, “Adaptive hierarchical representations in the hippocampus,”
Institute of Science and Technology Austria, 2024.
ista: Chiossi HSC. 2024. Adaptive hierarchical representations in the hippocampus.
Institute of Science and Technology Austria.
mla: Chiossi, Heloisa S. C. Adaptive Hierarchical Representations in the Hippocampus.
Institute of Science and Technology Austria, 2024, doi:10.15479/at:ista:14821.
short: H.S.C. Chiossi, Adaptive Hierarchical Representations in the Hippocampus,
Institute of Science and Technology Austria, 2024.
corr_author: '1'
date_created: 2024-01-16T14:25:21Z
date_published: 2024-01-19T00:00:00Z
date_updated: 2026-04-07T13:21:56Z
day: '19'
ddc:
- '570'
degree_awarded: PhD
department:
- _id: GradSch
- _id: JoCs
doi: 10.15479/at:ista:14821
ec_funded: 1
file:
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content_type: application/vnd.openxmlformats-officedocument.wordprocessingml.document
creator: hchiossi
date_created: 2024-01-19T11:04:05Z
date_updated: 2025-01-19T23:30:04Z
embargo_to: open_access
file_id: '14838'
file_name: PhD_Thesis_190124.docx
file_size: 8656268
relation: source_file
- access_level: open_access
checksum: 13adc8dcfb5b6b18107f89f0a98fa8bd
content_type: application/pdf
creator: hchiossi
date_created: 2024-01-19T11:03:59Z
date_updated: 2025-01-19T23:30:04Z
embargo: 2025-01-19
file_id: '14839'
file_name: PhD_Thesis_190124.pdf
file_size: 6567275
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file_date_updated: 2025-01-19T23:30:04Z
fulldoi: https://doi.org/10.15479/at:ista:14821
has_accepted_license: '1'
language:
- iso: eng
month: '01'
oa: 1
oa_version: Published Version
page: '89'
project:
- _id: 2564DBCA-B435-11E9-9278-68D0E5697425
call_identifier: H2020
grant_number: '665385'
name: International IST Doctoral Program
publication_identifier:
issn:
- 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
status: public
supervisor:
- first_name: Jozsef L
full_name: Csicsvari, Jozsef L
id: 3FA14672-F248-11E8-B48F-1D18A9856A87
last_name: Csicsvari
orcid: 0000-0002-5193-4036
title: Adaptive hierarchical representations in the hippocampus
type: dissertation
user_id: ba8df636-2132-11f1-aed0-ed93e2281fdd
year: '2024'
...