Magnetoencephalography, or MEG, is a sophisticated, non-invasive neuroimaging technique employed to measure brain activity. This advanced method works by precisely recording the tiny magnetic fields produced by the brain’s electrical currents. It allows researchers and clinicians to create detailed maps of brain function, offering insights into how different parts of the brain communicate and respond.
How a MEG Machine Works
The underlying science of MEG centers on the electrical activity within brain cells. When neurons become active, they generate small electrical currents. These currents, in turn, produce incredibly weak magnetic fields that extend outside the skull. A MEG machine is specifically designed to detect these faint magnetic signals, which are approximately one billion times weaker than the Earth’s magnetic field.
To capture these minute signals, the MEG system utilizes specialized sensors known as Superconducting Quantum Interference Devices, or SQUIDs. These SQUID sensors are housed within a helmet-like device placed over a person’s head. For the SQUIDs to function effectively, they must be cooled to extremely low temperatures, typically around -269 degrees Celsius (-452 degrees Fahrenheit), using liquid helium.
The entire MEG system operates within a specially constructed magnetically shielded room. This room is built with layers of high-permeability metals and aluminum, designed to block out all external magnetic interference. Without this shielding, environmental magnetic noise from power lines, electronic devices, or even the Earth’s natural magnetic field would completely overwhelm the brain’s subtle signals, making accurate measurements impossible.
Clinical and Research Applications
MEG technology offers distinct advantages in both clinical diagnosis and neurological research. In clinical settings, it plays a significant role in pre-surgical mapping, particularly for individuals with epilepsy. MEG can precisely localize the origin of epileptic seizures by identifying the specific brain regions generating abnormal magnetic signals, guiding surgeons to remove only the affected tissue.
The technology is also used before brain tumor removal to map out critical functional areas, such as those responsible for language, movement, or sensation. This pre-surgical mapping helps neurosurgeons preserve healthy brain tissue and minimize neurological deficits. By showing which areas are active during specific tasks, MEG provides a detailed functional roadmap for surgical planning.
For research purposes, MEG is invaluable for studying cognitive processes in real-time. Scientists use it to investigate how the brain processes language, forms memories, or interprets sensory information. Its ability to capture brain activity with millisecond precision allows researchers to observe the dynamic sequence of neural events involved in complex thought. MEG also contributes to understanding various neurological and psychiatric disorders, including Parkinson’s disease, autism spectrum disorder, and schizophrenia, by revealing subtle changes in brain network activity.
Comparing MEG with Other Brain Scans
MEG provides unique insights when compared to other established brain imaging techniques. Both MEG and electroencephalography (EEG) directly measure the timing of brain cell activity, offering excellent temporal resolution that shows when neural events occur. The main distinction lies in what they measure and how the skull affects those measurements. EEG measures electrical potentials on the scalp, which are distorted and smeared as they pass through the skull and scalp.
MEG, however, measures the magnetic fields generated by these electrical currents, and these magnetic fields pass through the skull and scalp without distortion. This characteristic gives MEG superior spatial localization compared to EEG, meaning it can more accurately pinpoint where in the brain activity originates. While EEG is more widely available and less expensive, MEG offers a more precise anatomical location of brain activity.
Comparing MEG with functional magnetic resonance imaging (fMRI) highlights different strengths. MEG directly measures the magnetic fields produced by neuronal activity, providing precise timing information about when brain activity occurs. In contrast, fMRI indirectly measures brain activity by detecting changes in blood flow and oxygenation that accompany neural activity.
The Patient Experience
Undergoing a MEG scan is generally a straightforward and comfortable experience. Before the procedure, individuals are typically asked to remove all metal objects, including jewelry, watches, hairpins, and certain dental retainers, as metal can interfere with the sensitive magnetic measurements. Clothing without metal zippers or buttons is also recommended.
During the scan, the person usually sits comfortably in a reclining chair or lies down on a bed, depending on the specific MEG system. The helmet-like MEG sensor array is then positioned over their head, without making direct contact with the scalp. The entire procedure is completely silent, a notable contrast to the loud noises often associated with MRI scans.
The MEG scan is painless and non-invasive, meaning it does not involve any injections, radiation exposure, or strong magnetic fields that interact with the body in a significant way. The process usually lasts between 45 minutes to an hour and a half, during which the individual is asked to remain as still as possible. They may be asked to perform simple tasks, listen to sounds, or respond to visual cues, depending on the purpose of the scan.