Magnetoencephalography (MEG) is a non-invasive neuroimaging technique that measures the subtle magnetic fields generated by the brain’s electrical activity. This technology allows for the mapping of brain function and the identification of activity associated with various neurological processes. MEG evaluates brain activity without exposure to radiation.
The Science Behind MEG
Brain activity involves electrical currents flowing within neurons, the brain’s specialized cells. These electrical currents produce tiny magnetic fields that extend outside the head, which MEG detects. These magnetic fields are extremely weak, often a billionth of the Earth’s magnetic field, necessitating highly sensitive equipment for their detection.
To measure these faint signals, MEG systems use specialized sensors called Superconducting Quantum Interference Devices (SQUIDs). SQUIDs detect and amplify these minute magnetic fields. The MEG system is housed within a magnetically shielded room to ensure accurate measurements, blocking external magnetic interference and allowing SQUIDs to detect only the brain’s intrinsic signals.
The MEG System and Scan Process
An MEG system typically includes a helmet-like sensor array that fits over a person’s head, containing hundreds of SQUID sensors. This array captures the magnetic fields emanating from the brain.
During an MEG scan, the person usually sits or lies down comfortably. They may be asked to remove all metal accessories and change into a medical gown to prevent interference with the sensitive magnetic detectors. Positioning coils might be attached to the head to help determine its location relative to the sensors. The sensors then record brain activity as the person rests or performs specific tasks, such as listening to sounds, viewing images, or making movements. The procedure typically lasts one to two hours.
What MEG Reveals
MEG provides detailed information about both the location and timing of brain activity. It allows researchers and clinicians to precisely pinpoint the source of neuronal signals within the brain and track how quickly these signals change over milliseconds. This combination of spatial and temporal resolution offers unique insights into brain function.
One significant application of MEG is in identifying the source of epileptic seizures. By localizing abnormal brain activity, MEG helps in planning surgical interventions for epilepsy. It is also used for pre-surgical mapping of brain functions, such as language, motor, and sensory areas, to help surgeons avoid damaging these regions during tumor removal or other procedures. In research settings, MEG is employed to study cognitive processes like perception, memory, and language, providing a window into how the brain processes information in real-time.
MEG’s Distinct Contributions
MEG stands out among neuroimaging techniques due to its direct measurement of neuronal activity through magnetic fields. Unlike methods that infer brain activity from changes in blood flow, MEG captures the direct electrical currents in neurons. This direct measurement contributes to its excellent temporal resolution, allowing it to detect brain events on a millisecond timescale, which is the speed at which neurons communicate.
The magnetic fields measured by MEG are not distorted by the skull or scalp, which provides better spatial accuracy compared to some other techniques that measure electrical signals at the scalp. MEG is considered safe for repeated use across various populations, including children. It offers complementary information to other imaging modalities, enriching the understanding of brain function by providing unique insights into the rapid dynamics of neural networks.