Magnetoencephalography

What is magnetoencephalography (MEG)? 

MEG uses a helmet-shaped device containing MEG sensors (gradiometers) to noninvasively measure the magnetic fields produced by neural activity of the brain. MEG is able to localise the source of neural activity to particular brain regions, represented as positive and negative charges (dipoles), with greater accuracy than EEG, which is a measure of the electrical fields produced by neural activity. MEG can be used to measure continuous resting-state brain activity (spontaneous MEG), but also to assess event-related changes in brain activity. Spontaneous MEG reflects neural activity in particular brain regions and across a range of frequencies. Delta frequency (up to 4 Hz) is slow wave activity normally seen during deep sleep; theta frequency (4 to 7 Hz) is often seen during drowsiness and early stages of sleep; alpha activity (8 to 12 Hz) commonly occurs during a state of relaxed wakefulness, particularly when eyes are closed; beta frequency (13 to 30 Hz) of low amplitude occurs during intense concentration and mental activity; and gamma frequency (30 to 80+ Hz) occurs during certain cognitive and motor functions. Change in activity is assessed as a dipole density, which measures the representation of each type of wave within a particular region.

What is the evidence on MEG?

MEG uses a helmet-shaped device containing MEG sensors (gradiometers) to noninvasively measure the magnetic fields produced by neural activity of the brain. MEG is able to localise the source of neural activity to particular brain regions, represented as positive and negative charges (dipoles), with greater accuracy than EEG, which is a measure of the electrical fields produced by neural activity. MEG can be used to measure continuous resting-state brain activity (spontaneous MEG), but also to assess event-related changes in brain activity. Spontaneous MEG reflects neural activity in particular brain regions and across a range of frequencies. Delta frequency (up to 4 Hz) is slow wave activity normally seen during deep sleep; theta frequency (4 to 7 Hz) is often seen during drowsiness and early stages of sleep; alpha activity (8 to 12 Hz) commonly occurs during a state of relaxed wakefulness, particularly when eyes are closed; beta frequency (13 to 30 Hz) of low amplitude occurs during intense concentration and mental activity; and gamma frequency (30 to 80+ Hz) occurs during certain cognitive and motor functions. Change in activity is assessed as a dipole density, which measures the representation of each type of wave within a particular region.

March 2019

Last updated at: 12:37 am, 28th March 2019
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