While not used in every fMRI study, a majority of the research
currently being done involves some form of auditory or visual stimuli being
presented to the subject while inside the MRI machine. This may seem like an
easy enough task to accomplish until you take into account the imitations of
working in an MR environment. The static magnetic field, which in a
superconducting magnet is always on, severely restricts almost every aspect of
stimuli presentation. One must also consider
the physical limitations that come with having your subject lying prone inside
of a magnet that has an approximate 56 cm diameter bore while their entire head
is encased in a coil. Once you begin placing the pieces together it becomes
apparent that circumventing these limitations is no simple task. I can’t recall
how many emails I have gotten over the years from former colleagues that,
although they were extremely comfortable with the setup and equipment in our
facility when they worked here, have no clue where to begin when it comes to
setting up their own facility. Of course each facility is different and modifications
must be made to accommodate for that, but these next few posts should provide a
good starting point for most.
Deceptively Simple: The Auditory and Visual Stimuli Systems
Let’s begin with two slightly deceiving images; audio and
video switch flow charts of the setup at my facility:
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| Figure 1 - Audio Switch Flow Chart |
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| Figure 2 - Video Switch Flow Chart |
I say these charts are deceiving because they give the
impression that the two setups are simple. And in many respects they are! But
the simplified look and approach are intentional. In fact the design philosophy
we follow at my facility is a minimalistic one focused on reducing conflict
between our user’s varying individual research requirements by offering plug
and play options alongside our stationary systems. By keeping this core idea in
mind from the very beginning we were able to construct a setup that accommodates
all of our users while leaving room for changes to be made on the fly. For example,
owning multiple button response boxes comes in handy when one randomly decides
to stop functioning in the middle of a session.
Continuing the idea of simplification, setting it all up to be
so unassuming is where the real challenge lies. The flow charts don’t take into
account the physical limitations I mentioned in the opening paragraph. Quite
frankly, they don’t tell you how the sausage is made! For most end users, that
is perfectly fine. In fact it is ideal. Less information overload means less
possible confusion during scans. On the day of a scan users just want to be
able to walk in, push a few buttons, and have everything ready to go. A smooth
and hassle-free setup makes it easier to focus on the science.
But let’s return to the two charts for the time being. As I
said before, their setup is actually quite simple; the input signal goes into a
mechanical switch, which is then fed to different outputs and it is up to the
researcher to utilize whichever ones are require. Understandably, you probably
don’t know what the display monitor or 32 channel ear buds are for -- but don’t
worry! I will be going into much greater detail about them in subsequent posts.
For now, all that is important to understand is the basic setup and, hopefully,
it’s gotten you to start thinking about possible issues that can arise.
Here are just a few concerns that may be raddling around in
your head after looking at those charts:
- Why are they using VGA inputs?
- Are all those inputs and outputs necessary?
- Does my facility need a similar setup?
- What switches/audio systems/projector are they using? Why those specific one?
- Was everything purchased? Built? Modified?
The list can go on and on, depending on your motivations for
reading this blog and wanting to know more. I’ll be doing my best to answer
these questions, and others that may arise, in subsequent posts. So keep them
in the back of your mind as we move forward.
