While you may often
read about the brain,
do you actually know
how it works?
LEFT - A neuron has
three main parts: The
Cell Body, Dendrites,
and Axons. You have
~ 100,000,000 of these
in your brain!
dendrite receives these chemicals, which
then change the amount of electricity inside of the cell body. Once the electricity is high enough, they send off a spike
and the process continues. Human and
insect neurons are remarkably similar in
their build and function, which allows us
to use insects to understand how the human brain works.
Recording electrical messages from
bugs is much easier than recording electrical messages from the human brain,
because bugs have a hard but thin exoskeleton (shell). By placing metal pins
inside an insect, you can amplify these
small spikes and “listen” to what the
brain sounds like. An affordable bio-amplifier costs ~$100 and can also be
used to send the audio of the brain signals into your iPad, PC, or smartphone
(Android or Apple). Once hooked up to
a device, you will be able to observe these
electrical messages as they travel down
the axons in real time. In a series of easy
experiments using a leg of a cockroach,
you can not only hear and see the action
potentials, but you can also learn how
they encode information!
RIGHT - Closeup of the cockroach leg showing the position of hair (barbs) all down the leg. Under each hair is a neuron. The neuron sends its axon to the brain.
The first experiment is easy. You can
use the Americana periplaneta (
American cockroach), Blaberus discoidalis (
discoid, or false death’s head), or
Grompha-dorhina portentosa (Madagascar hissing
cockroach). These species are large, easy
to handle, easy to maintain, and available
from many pet stores as a feeder insect.
Let’s get started. First we put a cockroach in some ice water to anesthetize
it. Insects are cold-blooded. So when we
place the bug into cold water, the neurons
stop firing. Therefore the bug will stop
moving and it won’t feel pain. If you ever
had a shot at the dentist’s office before
getting a tooth drilled, you know how
quieting the neurons works. Once the insect is out cold . . . we cut one of its legs.
The legs grow back; don’t worry! We need
the leg to warm back up to room temperature so that we can record its neurons.
Every cockroach leg has many, many
hairs on it, and under each of these hairs
lies a neuron. These neurons send electrical information (spikes) to the brain
about things that happen in the cockroach’s surroundings, such as wind,
touch, or vibrations of someone approaching. We can record spikes from
these neurons by sticking two metal pins
into a leg that we place on a cork. There
are so many axons in the leg that when
we place a pin randomly in the leg it will
be touching one of them.
Once you turn on the device, you can
begin to hear what these spikes sound
like. People describe this sound as being
similar to the sound of rain or popcorn
popping. If you then import the sound
into your iPad, you can look at the shape
of the spikes you are listening to. You
will notice that spikes take on a very
distinct down-up-down waveform. The
size of this waveform (the amplitude)
never changes. What does change is the
LEFT - Two pins are placed in the leg of
the cockroach. As spikes are sent down the
axon, the pins pick up the electrical activity
and amplify it!