Year: 2014
Type: dissertation
Abstract: This project is providing new evidence how normal hippocampal dependent memory and pathological processes are related to electrical activity of local neuronal populations know as local field potentials (LFP) or brain rhythms.The focus of the first study was to study how hippocampal rhythms are expressing temporal context, an important aspect of hippocampal dependent episodic memory system.We recorded LFP during a prolonged lever pressing task enabling us to reduce other behaviorally related brain activity.As we noticed single brain rhythms as such cannot predict whether a rat pays attention to lever pressing for reward.More likely, the dynamics between theta and gamma rhythms are more related to the outcome in this task.Similar results were obtained in a project in which we tested whether actually artificial electrical stimulation could improve memory or rescue it after lesioning nerve fiber bundles connecting hippocampus to medial septum.This lesion impairs memory in a hippocampal dependent memory task and abolishes naturally occurring theta rhythm.As we restored hippocampal theta by deep brain stimulation mimicking the amplitude and frequency of theta, we, surprisingly, observed no improvement but impairment in the memory.This impairment was as severe as the lesioning effect.As a conclusion, a single brain rhythm as such is not plausible crucial for normal memory functions.Rather, it is more likely that memory functions are related to more complex LFP dynamics involving several brain rhythms and their interactions.Clinical observations have so far implied increase in the slower frequency range in EEG during progression of AD.However, recent reports also point to neuronal hyperactivity in AD.It seems that a small proportion of AD patients also has epileptic activity, which makes them more susceptible to faster progression of memory impairment.Indeed, when we recorded LFP of transgenic mice expressing amyloid pathology, we observed already before plaque formation hyperactivity in thalamocortical area and changes in the hippocampal theta-gamma-synchrony.
Author: Arto Lipponen
Language: English
Subfield: Cellular and Molecular Neuroscience
Field: Neuroscience
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W3097317806