MEG stands for “magnetoencephalography” (“magnet-brain-picture”). It allows us to see which parts of your brain are being used for different types of tasks. MEG measures magnetic fields that are created by the brain’s electrical activity. With MEG we can look not only at where brain activity is happening, but when, with very high resolution in both time and space. As well as mapping out the normal activity of the brain, MEG can be used to evaluate conditions such as epilepsy, by uncovering which areas are involved in seizures.
One of the main advantages of using MEG is its simplicity. Unlike EEG, it doesn’t require electrodes to be attached to the skin. Instead, a person simply sits in a chair, resting their head inside the MEG helmet. Unlike MRI, the scanner is completely silent. MEG does not emit radiation or magnetic fields, meaning even people with pacemakers and medical implants can be scanned safely. People with metal implants near the head may not be able to participate, only because these items make it difficult to detect the brain’s signals. MEG is safe for all ages and groups of people.
A MEG scan can be completed in under half an hour. However, very small signals can take longer to find, and some scans can take up to an hour or more. Signals that originate near the skull are easiest to detect. This is because magnetic fields fade with distance, and sources near the center of the head are too far from the helmet’s sensors. Once these magnetic fields are detected they can be traced to their source. Using this information we can determine which parts of the brain are used for different mental processes or actions. We can also determine which parts of the brain are communicating with each other allowing us look at complex networks in the brain. New methods for reading MEG data are always being developed, giving us more information than ever before.
One of the unique aspects of MEG is the ability to watch brain activity change as milliseconds go by. Using this information, we can create slow-motion videos of the brain at work, and look at how signals change over time. Also, because magnetic fields are not blocked by the brain and skull, we can accurately find activity within millimetres. Instead of providing us with an image of the brain, MEG tells us where in space this activity is happening. By combining this with a brain image from an MRI, activity can be found in specific regions of a person’s brain, helping us to understand both the brain’s function and the causes of disorders.
Our MEG system is located at the IWK Hospital in Halifax.