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Magnetoencephalography
Last reviewed: 23.04.2024
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Magnetoencephalography - registration of the magnetic component of the electromagnetic field of the brain. This method arose relatively recently in connection with the successes of low-temperature physics and ultrasensitive magnetometry.
Magnetoencephalography is not only a non-invasive, but even a non-contact method for studying the functional state of the brain. Its physical essence lies in the registration of superweak magnetic fields arising from the flow of electric currents in the brain.
[How is magnetoencephalography performed?
The main sensor is an induction coil placed in a vessel with liquid helium to give it superconducting properties. It is located parallel to the surface of the skull at a distance of 1 cm. Only in this way can the weak induction currents appear in the coil under the influence of magnetic fields caused by the flow of extracellular currents parallel to the surface of the skull, the lines of force of these fields emerge radially (perpendicular to the surface of the skull).
The fundamental difference between the magnetic field of the brain and the electric field is that the skull and brain shells practically do not influence its magnitude. This allows one to register the activity of not only the most superficially located cortical structures (as in the case of EEG ), but also deep brain regions with a sufficiently high signal-to-noise ratio. For this reason, magnetoencephalography is particularly effective for the precise determination of the intracerebral location of epileptic foci and generators of various components of evoked EEG potentials and rhythms, especially since multichannel magnetoencephalographs have been created to date. It was for magnetoencephalography that the mathematical apparatus was first developed and software tools for determining the localization of an equivalent dipole source in the volume of the brain were created, which were then modified for a similar analysis of the EEG.
Despite the apparent advantages, magnetoencephalography and EEG are considered complementary methods of brain research. First, the equipment for recording the magnetoencephalogram is much more expensive than the EEG system. Secondly, the magnetoencephalography is extremely sensitive to the displacement of the sensor relative to the patient's head and to external magnetic fields, the screening of which is a rather complicated technical task. Thirdly, magnetoencephalography mainly records the activity of tangentially located dipoles (presumably neurons lying in the furrows), whereas the EEG reflects the activity of most of the cortical neurons both in the depth of the furrows and on the surface of the brain's gyri.