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TOM COSTELLO: A bird snatching a fish from the ocean, a frog
jumping from a lily pad, an artist painting a portrait - all
of these actions depend on the animal's nervous system, and at
the center of it is the brain, the vital organ that controls
all of an animal's thoughts, emotions and behaviors. Although
different species have brains of varying shapes and sizes, the
formation of all brains and their neural circuits follow a
similar developmental principles.
CARLOS AIZENMAN: It's vital to study brain development
in order to just understand normal development
but also abnormal development.
COSTELLO: Carlos Aizenman, a neuroscientist at Brown
University is funded by the National Science Foundation.
He’s trying to understand the basic biology of how neural
circuits develop. Neural circuits are made up of networks
of cells called neurons that generate electrical and
chemical signals in order to communicate with one another.
Each circuit is responsible for a different action or behavior.
These circuits are sculpted by how the animals interact
with their surrounding environments starting at the
earliest stages of life.
AIZENMAN: Say you're interested in studying how vision is
processed, there will be certain groups of neurons that form a
circuit that will be activated when you experience a certain
type of visual stimulus.
COSTELLO: To unlock answers about the development of neural
circuits, Aizenman and the students in his lab are studying
the simple structure and wiring of tadpole brains from a type of
frog called xenopus laevis, or African clawed frog. Their
brains are about four to five millimeters long and about just
one millimeter wide. Aizenman and his team are focusing on a
region of the tadpole's midbrain that is just .3 millimeters
wide, called the optic tectum, in order to understand
how experience from the tadpole's environment plays
a role in development.
AIZENMAN: In frogs, that is their main sensory processing
area. And if you look at a frog brain or a tadpole brain, you'll
see that one of the most prominent parts of the brain
are the optic tectum. And therefore, it must be very
important to the frog's survival.
COSTELLO: Tadpoles are bred in Aizenman's lab every week and
kept in an incubator at various stages of development, from two
days old to two to three weeks old when they are actively
exploring their environment.
TORREY TRUSZKOWSKI: This is a stage-49 tadpole. On either side
these dark spots are the eyeballs. Right here, this is
one nostril and here's the other one. And then underneath this
dark spot, these are pigmented melanocytes, so skin cells,
and underneath that is the actual brain itself.
COSTELLO: After extracting a tadpole's brain, students use a
technique called electrophysiology to probe
individual neurons with electrodes in order to amplify
and measure the electrical activity of the neuron.
TRUSZKOWSKI: What I’m recording here is the activity of the cell
in response to the stimulating electrode that I have placed on
the visual input pathway. There's tons of activity
going on here.
COSTELLO: Students also study the tadpole's behavior in a
collision avoidance experiment. This helps them understand the
state of the tadpole's visual networks, which are sculpted by
its experience early in life. During the experiment, a tadpole
is put into a petri dish on top of a monitor. A dot representing
the tadpole's predator is then projected onto the monitor
screen and moved towards the tadpole to elicit an escape
response. The students record the tadpole's behavior - swim
speed before the dot approaches and after the tadpole notices
the dot, as well as the distance between the tadpole and the dot
at the moment the tadpole notices the dot.
CAROLINA RAMIREZ VIZCARRONDO: By studying these behaviors, we can
characterize them, and when we expose tadpoles to certain
pharmacological agents, if they have different speeds or
different execution of this behavior, we can tell that there
is dysfunction at that particular circuit.
COSTELLO: By studying the tadpole's simple brain structure
and the way it processes information during the early
stages of life, Aizenman and his team hope to get one step closer
to understanding neural circuit development.
AIZENMAN: There's a lot going on in the developing brain. That's
why it's an interesting and remarkable process.
COSTELLO: A process that keeps neuroscientists like Aizenman
pushing for answers in brain development.
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