BORIS Theses

BORIS Theses
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The coordinating influence of thalamic nucleus reuniens on sleep oscillations in cortical and hippocampal structures – relevance to memory consolidation and sleep structure

Bozic, Ivan (2022). The coordinating influence of thalamic nucleus reuniens on sleep oscillations in cortical and hippocampal structures – relevance to memory consolidation and sleep structure. (Thesis). Universität Bern, Bern

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Sleep is a fascinating and a bit mysterious behavior. Not only do so called “higher” animals like mammals sleep but also simpler organisms like jellyfish display rhythmic periods of quiescence which are interpreted as sleep. Despite it being almost ubiquitous across the animal kingdom, the function of sleep is still not fully understood. However, we do know that especially the brain is important for the initiation and maintenance of that state and that it is highly active during sleep. There has been a special focus on electric neuro-oscillations where research over the last 90 years has revealed that the brain displays quite distinct oscillatory patterns during sleep and its specific functions are slowly being brought to light, such as memory consolidation and communication between different brain regions. For example, it has been argued that newly formed memories are either stored in the hippocampus or at least dependent on it for reactivation and are later transferred to the neocortex or become independent of the hippocampus while being stabilized in the cortex, with a portion of the thalamus, the nucleus reuniens thalami, being possibly involved in this process as it is an anatomical relay between cortex and hippocampus. The aim of my PhD project was to investigate the coupling of neuro-oscillations between prefrontal cortex, thalamus, and hippocampus in both a descriptive and manipulative way. Namely, we investigated the coupling between prelimbic cortex, nucleus reuniens of the thalamus and the CA1 portion of the hippocampus during unperturbed natural sleep, sleep after sleep deprivation and sleep with increased mnemonic demands after a learning task. Lastly, we optogenetically manipulated nucleus reuniens during sleep to assess its properties as a synchronizing link between prefrontal cortex and hippocampus. We described the coupling of corticothalamic slow waves and spindles with ripples in the hippocampus by quantifying the amount of co-occurrence of the aforementioned events, describing the phase-locking of ripples to slow waves and spindles, and determining which oscillations drives the other. Next we found that spiking behavior of nucleus reuniens is coupled to ripples and cortical slow waves. Lastly, optogenetic manipulation showed that nucleus reuniens is involved in the precise phase-event coupling, in the co-occurrence of the mentioned events, and oscillatory drive between cortex and hippocampus. However, the effects we found on the neuro-oscillatory coupling were not accompanied by a change in memory performance after a learning task.

Item Type: Thesis
Dissertation Type: Cumulative
Date of Defense: 26 October 2022
Subjects: 600 Technology > 610 Medicine & health
Institute / Center: 04 Faculty of Medicine > Pre-clinic Human Medicine > BioMedical Research (DBMR) > DCR Unit Sahli Building > Forschungsgruppe Neurologie
Depositing User: Sarah Stalder
Date Deposited: 12 Jul 2023 06:36
Last Modified: 26 Oct 2023 22:25

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