Backyard Brains presents a new experiment: How to stimulate nervous
and muscle system tissue easily!
The equipment you'll need is a cockroach, with which you will take a leg
for your experiment;
a signal generator such as an iPhone with which to deliver stimuli to your
cockroach leg; a Y-splitter that splits the output of your signal generator to
an external speaker to hear your stimuli; and a cable that terminates in alligator
clips that attach to needles you implant in the cockroach leg
for your experiment.
Since the music that comes out of an iPhone or any kind of music
player is nothing more than electrical waveforms, what if we have the output of the
iPhone go directly to the cockroach leg?
Whoa! Now, notice I also have the iPhone hooked up to an external speaker so you can
hear the stimuli being delivered.
This demo immediately grabs students' attention and can lead into a discussion of how to
excite nervous and muscle system tissue.
Let's take a closer look.
Now, using hip-hop music to excite a cockroach leg is all well and good, but
let's try to do some serious observations and measurements on the
excitability of the muscle and nervous system tissue within the leg.
I've downloaded a signal generation program called freqGen onto my iPhone which allows
me to play biphasic,
square pulses of a variety of frequency and amplitudes and deliver such to the leg.
Now, there are many free, signal-generating programs out there on the internet
that will work on your computer or phone,
just google it.
So you can see at about
two thousand Hertz I'm playing with the amplitude, or volume
and it has varying degrees of effects on the excitability of the leg.
Now, if I drop the frequency down to twenty Hertz,
I see with very very small volume I can get contraction of the leg.
I can start systematically mapping the best frequencies and lowest amplitudes required
to excite the leg, and I'm doing the sort of experiments graduate students typically do
and get papers published on, but here I'm doing it in my basement on
my table top with minimum of equipment. You can do it too!
Oscillating at 20 Hz.
Now, you can see in the Backyard Brains lab book I've mapped up which volumes and
frequencies cause excitation of the cockroach leg,
and you can see at the high frequencies we get no movement regardless of the
volume, whereas at twenty hertz we get very nice movement across all amplitudes.
Now, you're probably thinking what does this mapping of amplitude and frequency
in a cockroach leg have to do with anything?
Well, microstimulation techniques of this kind are actually used in human patients
for Parkinson's disease and deep brain stimulation,
and functional electrical stimulation, whereby muscles of paralyzed patients are
excited with electricity.
Now, you may notice over time throughout your experiments, that the leg's responsiveness
to electrical excitation decreases over time.
This could be due to the leg dying
or habituation, both interesting hypothesis.
So I often, throughout my experiments, will check to see if I still get
evoked discharge of spikes
from the leg.
You can see I'm removing the excitation cables,
turning the SpikerBox on...
The leg is still alive.
You can also try this microstimulation experiment on a variety of other organisms
including grasshoppers, which are quite nice because they have very large muscles in their
hind, jumping legs.
Please, do let us know what you come up with.
Happy neuroscience, and happy discoveries!