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[CARRIE] When the subject first comes in, we explain
to them that we are going to clean some spots and put some electrodes on in order to measure
the electrical activity of their brain. And then we bring them into this room here.
So we have them come into this room and we have them put this helmet on. And we have a bunch
of, sort of hardware on it that holds the sources and detectors in place.
So what we are doing is we are shining near-infrared
light, which is a really low-level of light, through these fiber optic cables. And we are
just putting them on, we are just using this helmet to keep them into place, and they just
sit on the scalp. So we have got these, they are just sort of blunt tipped on the end,
and we put them into the holes and they just sit on the person's scalp like that during
the experiment and just shine a really low level of light into their head and brain.
And then we pick the lights up with these
bigger fibers; these detectors. And they go into these bigger holes here. And they do
the same thing. They just sit on the scalp. We do use a little tool to move the hair out
of the way because hair can absorb the light.
They have done a lot of studies in cells and they have found that when neurons are active,
they swell and become more transparent. And so the light actually goes deeper when the
cells are active.
Light goes down really only about a centimeter into the brain. So we are just sort of measuring
the activity on the very outside of the brain. And then we are just picking this light up
again with these detectors. And whether the brain is active or not you can tell by how
fast it takes the light to go from the light source to the light detector.
It may look a little bit scary because we
do have this whole helmet covered with the light sources, which are thin, and the light
detectors, which are thicker. But really they are just sitting on the scalp and the subject
is wearing the helmet and just doing the task. They can move around normally and it is not
painful or anything. You actually get less light this way than you would if you were,
say, standing outside on a sunny day. So it is a really low level of light.
People seem to do pretty well with it. Maybe
it is partly because they cannot see themselves once they are all set up, unless we take a
picture of them. [LAUGHS] But, yeah. Most people are pretty fine with it.
[GILBERT] It is not intimidating to me to have
to have the electrodes attached and the other types of devices, and spots cleaned, and things
glued to you, sensors glued to you. That is not really a problem. It does not hurt in any way.
[LAUGHS] And it is just part of what it takes to be a part of the study. So it is just an
interesting process that you have to go through to be a part of the study.
[CARRIE] The graphs on the screen will actually show us
how much light we are getting
from each of the detectors, so we can adjust them to the right levels. So, for some people,
we are getting too much light and we are, sort of, overexposing our equipment and then
we have to turn it down. And so we can, adjust the level of light. Older adults
are actually better to run in that respect, because they have less hair and lighter colored
hair often. And we get better light signals from older adults than we do from younger.
So we like running older adults better. [LAUGHS]
These are our optical machines right here. And actually they have both the light source,
as well as the light detectors in them. We have a lot of them, so we can record from
pretty much the whole head at the same time. These smaller ones down here are actually
the light sources. So each one of these is a laser diode. So it emits a little red light,
sort of like a laser pointer, and then it goes into one of these fiber optic cables.
So, if you have seen one of those fiber optic Christmas trees, these are pretty much the
same sorts of cables -- just sort of a higher tech version of that.
These bigger, black cables are the detectors.
So they are a whole bunch of those little ones bunched together. And what they are doing
is carrying the low levels of light back from your scalp, back into the machine. And so
the end of them is a little bit bigger, but it is really just a bunch of those cables
bundled together and they also just sit right on the scalp and we can pick up the light
from your brain and your head and then it carries it back into the machine where it
is then processed. And, from that, we can pretty much cover the entire outside of the
brain and figure out where and when activity is happening.
When you go into an MRI and you are actually
measuring the brain activity, you are actually measuring the blood flow. And it takes several
seconds for that to happen. We know that the brain is much faster than several seconds.
Things happen within milliseconds. And you cannot really measure that with MRI. And so
this technique actually, we can get both good, millisecond time resolution. But we can also
know where things are happening. We are actually measuring the activity of the cells of the
brain, the neurons, pretty quickly and so we can get a pretty good time resolution.
So we can tell when something is happening and where it is happening.
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