Your Brain is a Magnet?

When you perform any activity, different areas of your brain communicate with each other through electrical impulses. These impulses can also be thought of as electric currents. The famous physicists Maxwell and Faraday showed that any current will generate electric and magnetic fields. Thus, when your brain is active it creates tiny magnetic fields inside and around your head. This goes on all the time - when you are walking, talking, or even sleeping - but the fields are very small, so we don't notice them. For comparison, the ticking of an analog clock generates a magnetic field which is one million times larger! Our scientists are very interested in determining which areas of your brain are working while you perform different tasks. This is where Magnetoencephalography (MEG) comes in. As explained, we can think of patterns of brain activity as a number of sources of electro-magnetic fields. MEG allows us to measure the magnetic fields outside of your head. MEG is a non-invasive and passive way to measure the magnetic fields that your brain generates naturally. This method is non-invasive because it does not require making measurements inside your body. It is passive because it simply measures a signal that your brain generates, and does not act upon your body in any way. This method is used in hospitals and medical centers, is very low-risk, and has no known short or long term side effects.

For What Are We Looking?

The study of pictures of brain activity is a discipline known as Neuroimaging. In general, to generate a neuroimage, a person is placed within an imaging device (for example, MEG or MRI), and asked to observe some visual, auditory, or tactile stimulus. The person may be asked to perform a task, to think about the stimulus, or to do nothing. In some cases, the person is simply required to go to sleep! At our site, the magnetic field around the head is recorded at 151 locations at speeds up to 2500 samples per second. These 151 sets of magnetic field information (MEG data) are put through some mathematical modelling to estimate the location of the activity within the brain.

In the simplest cases, we may be trying to locate the brain centres associated with perceiving different types of objects with our eyes and ears, or by touch. More complex information processing such as melody and language can also be explored. Furthermore, we can look at which regions of the brain are involved in decision making, emotion, learning, and more.

Is MEG the Same as MRI?

Magnetic Resonance Imaging (MRI) is a much more well-known type of neuroimaging method. Basically, this method generates a 3-D picture of the density of brain matter. In essence, it is like removing the skull, and looking directly at the brain (as an X-ray allows us to look at bone structure under the skin). In order to achieve this, the person's upper body is placed in the centre of a large magnet. The magnet is rotated around the body and we observe the manner in which brain matter interacts with this large changing magnetic field. This is an "active" form of imaging, since we must apply a force on the person being measured.

In many ways, MEG is the opposite of MRI. Rather than applying a magnetic field to the brain and observing its effects, MEG measures naturally occuring magnetic fields generated by the brain. An MRI image gives us information about structure of brain matter, and sometimes how the blood-oxygen level of brain tissue changes over time. From these changes in blood-oxygen level, we can determine where blood flow changes are occuring in the brain. However, MEG allows us to localise the electrical impulses of brain activity directly. Thus, in many ways, MEG and MRI are complimentary forms of neuroimaging. The information about the structure of an individual's brain (obtained by MRI) can be combined with the brain activity location information (obtained by MEG) to generate a picture of which part of the brain is responsible for a given task.

So Who Makes These Machines Anyway?

The Rotman Research Institute MEG device is designed, manufactured, and maintained by CTF Systems Inc. CTF is a Canadian company based in Port Coquitlam, British Columbia. The device is most often and most accurately described as a "very large hair-dryer". A person sits on a adjustable hydraulic chair. The bottom of the device is shaped like the inside of a helmet. This is where the person's head is situated. One hundred and fifty-one magnetic field sensors are contained within the helmet. The electronic equipment which measures and amplifies the magnetic sensor information is contained in a large dewar above the helmet which holds almost 100L of Liquid Helium.

In order to measure the miniscule magnetic fields generated by the brain, the equipment in the dewar must be kept at very low temperatures (about -269 degrees Celsius). Helium is always at this temperature in its liquid state, so the dewar is filled with Liquid Helium to keep the electronic equipment cold. Because of the cryogenic design of the dewar, the inside of the dewar is only four degrees above absolute zero, but the outside of the dewar is quite comfortable to touch.