So there's this thing in your head called a brain, and it seems to be where thoughts
and feelings and memories and perceptions and everything elses happen, so it would be
great to know how it works. The obvious way to see how something works is to pull it out,
open it up and have a look, but when you do that with a brain, it stops working, and tends
to upset its owner, so what we really need are ways to study brains while they're working
inside people's heads. Which... isn't easy, but can be done with a range of different
brain imaging techniques. One of the popular techniques is MEG, magnetoencephalography,
which is much less scary than it sounds. Magneto means magnetism, encephalo means brain, and
ography means images, so magnetoencephalography means images of the magnetism of the brain.
'Cause the brain is made up of billions of cells called neurons. When the brain does
stuff, these neurons are sending electrical signals to each other, which, like all electrical
signals, generate magnetic fields. Magnetoencephalography measures and locates these magnetic fields,
which indicate the electrical activity of the neurons, which is the activity of the
brain. With magnetoencephalography, we can see the brain working, as its working, inside
someone's head. The magnetic fields caused by brain activity
are tiny and faint so we measure them with highly sensitive magnetism detectors called
SQUIDs, just like you’d use a highly sensitive microphone to measure a very quiet sound.
If you were measuring a very quiet sound you’d have to do in a very quiet room or else you
couldn’t hear the sound over the noise of air conditioning next door and cars down the
road – and you get the same problem detecting the brain’s magnetism over the magnetism
coming from nearby phones and computers and from the earth itself. To block out this noise,
MEG is performed in a shielded room built with thick layers of metal that block magnetic
fields from outside. Another complication is that SQUIDs, our super-sensitive magnetism
detectors, only work when they’re cooled down to about minus 270 degrees Celsius, which
is almost the absolute coldest it is possible for anything to be. Liquid helium can be used
to keep the SQUIDs this cool. The SQUIDs are then arranged in a sort of a helmet, with
a few hundred of the detectors held right up close to the head. Some specialised systems
have smaller helmets to better fit children. The SQUIDs do need to be close because they
can only detect brain activity a few centimetres into the brain, and even then only some kinds
of brain activity. But overall, MEG is still a pretty great brain imaging
technique, partly because the process is so easy. The subject just sticks their head in
the helmet, lies very still, and a detailed record is made of their brain activity. It’s
non-invasive, meaning we don’t have to cut anyone open, or inject anything, or expose
anyone to radiation, which a lot of the other techniques do involve. It also has really
good spatial and temporal resolution, meaning it captures a lot of detail and can do so
thousands of times per second so we can see changes in the brain moment-by-moment. Techniques
like EEG have less detail, and MRI can only take an image every second or two. It’s
important to keep in mind, though, that MEG doesn’t show the physical structure of the
brain – just its activity – so MEG scans are often combined with MRI scans so we can
see both together. But yeah. MEG has a lot of advantages as a brain imaging technique,
and because of these advantages, it’s widely used in research and diagnosis, where it can
show which bits of the brain are active when people do different things, and which parts
of the brain aren’t working in patients. Some of the really cool things you can do
with MEG include brain-computer interfaces, where a computer can monitor and respond to
brain activity. In one study, a computer was set up to move a cursor on a screen when a
particular kind of brain activity was detected by MEG. Stoke victims who couldn’t move
their hands learned to produce that kind of brain activity – so they were able to move
the cursor with their minds. When the computer was connected to a mechanical hand, the stroke
victims could open and close the hand with their brain activity. Similar stuff has been done
with monkeys controlling robotic arms. With this kind of technology, we can potentially
restore movement to people who can’t move, and communication to people who can’t speak.
We can even work out what people are seeing and thinking by measuring their brain activity.
Much of this kind of research involves implants in the brain rather than MEG, but it’s great
when MEG can be used because it’s so easy and non-invasive. But yeah the point is that
technologies like MEG are taking us closer and closer to Luke Skywalker robot-hands and
mind reading. In summary, magnetoencephalography works by
using super-sensitive magnetism detectors called SQUIDs to measure and locate the electrical
activity of the brain. You’ve got to do it in a shielded room, and with special cooling,
but it’s relatively easy to do, and it has great spatial and temporal resolution.
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