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The role of network bursts in memory

Antunes dos Santos Dias, I. (2019) The role of network bursts in memory.

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Abstract:In the awake state, memory acquisition is thought to be underlined by high cholinergic cortical levels, which allow the incoming information to be encoded in the hippocampus. During slowwave sleep, in a process known as systems consolidation, the encoded input is replayed by the hippocampus, which activates neocortical areas leading to the transfer of information to the cortex, where memories are permanently stored. This consolidation process, which results in persistent functional changes representing an experience in the brain, is believed to benefit from the oscillatory rhythms and the low acetylcholine availability observed in the neocortex. Few studies have empirically tested the previous hypothesis, with an unceasing debate on the mechanisms behind memory consolidation and retrieval. Our goal was then to better clarify if cholinergic modulation and synchronized activity are indeed essential for memory consolidation. We mimicked the cue replay observed during systems consolidation through lowfrequency electrical stimulation of dissociated cortical cultures bursting spontaneously, as observed during slow-wave sleep. We also applied the electrical stimuli replay in cultures treated with carbachol, a cholinergic agonist, to simulate the increased cholinergic tone observed in the awake cortex. We assessed the effect of both chemical and electrical stimulation on the activity and connectivity patterns of the cultures tested. Our results show that carbachol administration transformed activity patternsfrom synchronized bursting into dispersed uncorrelated firing. In cultures without carbachol treatment, we observed significant connectivity changes upon first stimulus application (p<0.05), while subsequent stimuli did not perpetrate any further changes in network connectivity (p>0.05). Moreover, application of a different stimulus led again to significant connectivity changes (p<0.05), which did not erase the first alterations observed. Distinctively, in carbachol-treated cultures we did not observe any significant connectivity drives away from baseline values (p>0.05), although cultures still responded to stimulation throughout the duration of the experiments. These observations suggest that cholinergic activation and the absence of synchronous activity hamper memory consolidation in dissociated cortical cultures. The present findings represents a step forward towards more profound proofs-of-concept regarding the underpinnings of memory replay and consolidation during slow-wave sleep.
Item Type:Essay (Master)
Faculty:TNW: Science and Technology
Subject:44 medicine
Programme:Biomedical Engineering MSc (66226)
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