Year: 2012
Type: dissertation
Abstract: Introduction, aims and outlineNode 1 other neurons.Instead of stimulating other neurons to fire, they can also inhibit the firing of others.So, the brain contains an enormous network of elements that are constantly stimulating and inhibiting each other.Since firing (groups of ) neurons essentially show repetitive, rhythmic behavior, they are often described as oscillators.Coupled oscillators influence each other, causing their firing rates to fasten, slow down or even stop.A mechanism that is presumed to be vital to neuronal interaction is synchronization: when (groups of ) neurons synchronize, they become more effective, and will exert a greater influence on their environment 2 .The selective routing of information needed to coordinate brain activity is realized by synchrony, and the level of synchronous firing between neuronal groups can be interpreted as the level of communication between them.When many neurons fire, oscillate and synchronize, they generate an electromagnetic field that can be detected outside the human head.Whereas electroencephalography (EEG) records the electric component of this field, magnetoencephalography (MEG) records the magnetic part.Both EEG and MEG can measure variations in brain activity at the scale of milliseconds.However, there are a few obstacles: first of all, the muscles, eyes and heart and even surrounding equipment, cars, buildings, etc. all produce electromagnetic fields that can distort the recording.Their influence must be minimized, and the use of shielded rooms and artifact filters are therefore important.Second, since EEG and MEG measure brain activity from the outside, there is uncertainty about the exact location of the activity source.Although mathematical techniques can be used to locate sources, there is no unique solution to this so-called inverse problem.A third important aspect is that since different EEG and MEG sensors pick up activity from common sources, computations of the strength of synchronization and thus communication between them is overestimated.This issue is called volume conduction, and it will be discussed later on in this thesis. Magnetoencephalography (MEG) system in upright position (source: Elekta ®)Advantages of MEG over more traditional EEG are the cleaner signal, higher level of detail, and a shorter preparation time.Disadvantages are the necessity of a shielded room, immobility, and high cost.Like EEG, MEG is completely non-invasive, silent, and it does not require radiation or strong magnetic fields.
Author: Willem de Haan
Language: English
Subfield: Cognitive Neuroscience
Field: Neuroscience
Domain: Life Sciences
Open Access status: green
Funder: Alzheimer Nederland
OpenAlex ID: W42187677