What does MEG measure?
MEG measures the magnetic signals produced by activity in your brain. These signals are very small (on the order of femtotesla, or 10-15). By comparison, your heartbeat produces a signal in picotesla (10-12). The earth's magnetic field is on the order of tens of microtesla (10-6). A technology such as magnetic resonance imaging (MRI) uses magnetic fields up to 3 Tesla (a signal 3,000,000,000,000,000 stronger than the signal produced by your brain).
Is undergoing MEG risky?
MEG is a passive tool for looking at magnetic activity in the brain. Unlike technologies such as functional magnetic resonance imaging (fMRI) or positron emission tomography (PET), MEG does not "put" anything into you. Rather, it records the magnetic activity that your brain naturally produces. There are no known risks associated with MEG.
What is the MEG machine like?
Because magnetic signals in the brain are so small, we must do everything possible to screen out electric or magnetic noise that would interfere with recording brain signals. Therefore the actual experiment takes place inside a Magnetically Shielded Room (MSR), which is rather large (about 8' wide by 8' high by 12' long), and contains a bed where you recline during testing.
Your head rests on a dewar containing the superconducting MEG sensors and liquid helium to keep them at the correct temperature. These sensors measure the activity in your brain while you look at words or pictures on a screen above your head, or listen to sounds or words through ear buds. There are no loud noises while the machine is recording, unlike MRI, so you may not even notice that anything is happening. The experimenter will try to make you as comfortable as possible.
What happens during the experiment?
Before the experiment begins, we do two things. First, we attach five small electromagnetic markers to your head. We do this so that we can figure out where exactly your head is when it is underneath the MEG sensors (this is something we can't guess about, or use a rough estimate of; the brain is very specialized, and two regions an inch apart can have very different functions). This is a painless process, and poses no danger. When these electromagnets are activated, for about 1 minute during each experiment, they are much weaker than refrigerator magnets, and slightly stronger than the magnetic signal of your heartbeat.
Second, we need to trace the shape of your head. We do this for two reasons. The most important is that the algorithms we use to figure out which parts of your brain are active are relatively dumb: they don't care much if they find something inside or outside your head. We, on the other hand, assume that most of the activity in your brain actually occurs in your brain, so we use the shape of your head to constrain the algorithms. When we later try to figure out what parts of your brain are active, it is much easier to understand the results if they are situated inside something that looks like a head, rather than just floating around in space, so we also use head shapes for graphic displays. We record your head shape using special digitizing equipment. This equipment records, in 3-dimensional space, where your head is as we "paint" a laser over it; interestingly, this equipment is also used in virtual-reality technology.
Once those two steps are completed, the experiment moves into the shielded room. There, you will lie down while the experiment takes place. The experiments can be of a variety of different designs. Some will look at language processing either with visual or auditory stimuli. Some experiments look at different cognitive functions again either with visual or auditory stimuli. You may be asked to respond to the stimuli with a button press or vocally or you may just be asked to lie still and try to stay awake.
Why are there such strict requirements for eligibility?
Most of our restrictions on participation relate to the fact that MEG measures magnetic signals in the brain, which means that any other magnetic materials near the MEG machine will interfere with our recording. It is important to note that magnetic materials are not at all dangerous around the sensors, but simply result in lower-quality data.
For this reason, we require that participants remove all watches, earrings, and other jewelry. Eyeglasses are also not permitted; participants must therefore have normal vision or use soft contacts. We may also ask you to remove belt buckles, keys, etc., before beginning.
Many types of cosmetics contain traces of iron -- in particular, some hair gels and coloring mousses, as well as mascara and rouge-- so makeup is to be avoided.
Clothing that contains metal (especially bras with metal underwire or clasps and shirts with metal zippers or buttons) cannot be worn in the shielded room. The fly on a pair of pants is permitted. We ask that, if possible, you wear clothing without metal, but can provide appropriate garments to change into if necessary.
Volunteers with permanent magnetic objects on the body (e.g., braces, permanent retainers, etc.) may not participate. Most fillings and crowns are fine.
NYU Department of Psychology
6 Washington Place, Room 284
New York, NY 10003
The MEG lab is located in the Meyer Complex on the NYU Washington Square Campus on Washington Place between Broadway and Mercer Street.
Detailed directions to campus via subway, bus, or car
Once you arrive:
Sign in at the front desk.
Walk past the right side of the desk and down the hallway.
Take the elevator on your left to the second floor.
Take an immediate left when you exit the elevator.
Look for the MEG Lab sign on your right.
If you have trouble finding the lab, you should call the phone number provided by the experimenter who scheduled your session, or call Jeff Walker, the MEG lab manager, at 212-992-7462.