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About the MEG
Peering into the Brain At the DSRF we have a specialized imaging tool that records these small magnetic fields called magnetoencephalography (MEG). The MEG installed at DSRF is a 151-channel whole cortex system manufactured by CTF Systems, Inc. (Canada). The system is placed inside a magnetically shielded room that protects it from the strong environmental fields such as the Earth field, industrial electromagnetic noise, etc. We use the MEG to conduct numerous studies . How does the MEG work? The liquid helium vessel has a helmet-shaped bottom and the sensor array inside the vessel follows the shape of the helmet. When a person sits inside, their head is placed in the helmet with the sensors very close to the scalp to allow the detection of the electromagnetic activity of the brain. MEG is a completely non-invasive technology. It does not involve any physical, electromagnetic or chemical intervention with the subject. The system is just passively “listening” to the natural brain activity. This technology is particularly suited for children and other populations who may be more sensitive to noise and small confined spaces. What happens once the information from the brain has been collected? Looking at this data we can get some basic information about the signals and how these signals change with different conditions. For example this image shows 3 examples displaying the signals when a person is sitting quietly with their eyes closed (A), eyes open (B) and when they are looking at an image on the computer screen (C). The qualitative differences in the rhythms of the brain under the different conditions are quite apparent in these plots. Once we have looked at these plots we use sophisticated signal processing methods to estimate the location of the activity within the brain. This is referred to as the inverse problem. The main issue is that the inverse problem does not have a unique solution. In other words there are many, many possible solutions to where the activity is located in the brain. Our signal processing scientists use various models and techniques that are based to find the best solution. These models are based on specific assumptions that are made about the shape of the head, knowledge about neurophysiology, etc. Once the locations of brain activity are determined, we then look at the relationship between different locations and the timing of this activity. Below is a figure that shows the areas of activation during a motor task involving pressing a button with the index finger. The top plot shows the average from a group of typically developing adults; the bottom plot shows the average from a group of adults with Down syndrome. Differences and similarities in the active areas of the brain between the two groups can be clearly seen.
Useful Links: Follow these links to learn more about magnetoencephalography.
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No matter what we do, or even when we seem to do nothing our brain keeps working. Hundreds of thousands of neurons are firing resulting in tiny electrical currents running inside various parts of the brain. These currents could tell us a lot about what is going on in the brain, but we cannot measure them directly. However, electric currents in the brain (red arrow) generate magnetic fields (blue arrow) which easily penetrate the brain tissue and emerge outside the skull. These magnetic fields are extremely small.
Once we collect the information from the MEG, the real work begins! Our scientists first look at the data to look at the overall signals from the brain. On the right is an example of what the signals look like from each of the 151 channels. Each line represents a single channel of information from a particular part of the brain progressing over time.
1409 Sperling Avenue, Burnaby
British Columbia, Canada
V5B 4J8
fax: +1 604 431 9248
email: info@dsrf.org
