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TOM COSTELLO: Learning from experience - in the animal
kingdom it can mean the difference between life and
death. From eagles to whales to humans, animals use the
information they learn in their environment each day, changing
their actions to aid in their survival. And it's all due to
one of the most mysterious organs we all possess:
the brain.
GARY LYNCH: The brain is essential to all activities, of
course. But the thing that separates it from all other
organs is this incredible ability to absorb information
from the world.
COSTELLO: Dr. Gary Lynch is a neuroscientist at the University
of California, Irvine. With funding from the National
Science Foundation, he is researching what lies behind
the brain's ability to learn and remember.
LYNCH: Every instant of the waking day you're
accumulating information.
COSTELLO: To process, organize, and store all the information,
the brain employs cells called neurons. Neurons are basic to
all brains, from roundworms to humans. When a puppy sniffs out
a new playmate, or a panda discovers snow, the information,
in the form of electro-chemical signals, is received by the
neuron's antennae-like dendrites, processed in the cell
body, and then passed along through the axon to the next
cell in just a fraction of a second. In a human brain, the
neuron connects to as many as 10,000 other neurons, which
connect to thousands of other neurons, creating a vast
communication network throughout the brain.
LYNCH: So when you think about the neuron, the big antenna
and the long wire, you can begin to get the picture of
the web being built.
COSTELLO: Neurons communicate with each other through a
junction called a synapse, where information signals are
transmitted and received. An electrical signal, called an
action potential, travels down the axon of the "talking" neuron
until it reaches the axon terminal, releasing chemical
neurotransmitters into a minuscule gap. Spines on the
dendrites of the “listening” neuron have special protein
receptors that bind with the neurotransmitters. This complex
messaging sequence is repeated by the thousands every second.
LYNCH: So just think of that. Twenty-four hours a day
throughout your life, fifty billion of these things are
doing this and you get an image of the complexity.
COSTELLO: If the same signal is repeated several times, as with
training or practice, more synapses are affected and
synaptic communication becomes stronger. So animals can recall
which foods to eat, where to find water, and how to get
home from work - everything animals learn from interaction
with the environment.
LYNCH: And so your memory is becoming more and more secure
because more and more neurons, more and more of the synapses
have got that information.
COSTELLO: Not only can synapses get stronger, but they can also
get weaker or even disappear, depending on how often the
synapse is used. Communication between neurons is altered by
changes in the amount of neurotransmitter released, the
number and sensitivity of the neuro-receptors, and the
number and shape of dendritic spines. This means that the
brain is continually building, pruning, and reshaping the
network of neurons. In his lab, Lynch demonstrates this by
passing electrical impulses through the brain of a rat.
When the signal travels through the synapse, he is able to
measure and record the voltage the synapse receives. When the
signal is repeated, it generates a larger voltage, signifying a
stronger synaptic connection. Lynch explains that this is
because the dendritic spines are changing shape, allowing for
stronger synaptic communication.
LYNCH: When it sends that message, this spine, this
dendritic receiver morphs and, if everything goes right, it
will morph into a state that forever afterwards, when the
message comes, it generates a bigger voltage.
COSTELLO: Much of the brain's dynamic synaptic structure still
remains a mystery. But Lynch and his team are determined to
unlock the secrets of learning and memory.
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