[MURG] [>Htech] sciencedaily: watching fly neurons get classically conditioned (fwd from alito@organicrobot.com)

Tue May 18 10:31:27 EST 2004

----- Forwarded message from Alejandro Dubrovsky <alito at organicrobot.com> -----

From: Alejandro Dubrovsky <alito at organicrobot.com>
Date: Wed, 19 May 2004 01:41:25 +1000
To: transhumantech <transhumantech at yahoogroups.com>
Subject: [>Htech] sciencedaily:  watching fly neurons get classically conditioned
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(
method more interesting than the results
http://www.ninds.nih.gov/news_and_events/pressrelease_memory_051204.htm
)

Study in Flies Allows Researchers to Visualize Formation of a Memory
For release: Wednesday, May 12, 2004

Overview For the first time, researchers have used a technique called
optical imaging to visualize changes in nerve connections when flies
learn. These changes may be the beginning of a complex chain of events
that leads to formation of lasting memories.

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For the first time, researchers have used a technique called optical
imaging to visualize changes in nerve connections when flies learn.
These changes may be the beginning of a complex chain of events that
leads to formation of lasting memories.  The study was funded in part by
the NIHs National Institute of Neurological Disorders and Stroke (NINDS)
and appears in the May 13, 2004, issue of Neuron.1

Scientists have long been captivated by the questions of how memories
form and how they are represented in the brain.  The answers to these
questions may help researchers understand how to treat or prevent memory
problems, drug addiction, and other human ailments.  Thousands of
changes in gene expression, neuron formation, nerve signaling, and other
characteristics may be involved in the formation of just a single
memory.  Scientists refer to any learning-induced change in the brain as
a "memory trace."

In the new study, Ronald L. Davis, Ph.D and colleagues at Baylor College
of Medicine in Houston developed fruit flies with special genes that
caused the flies neuronal connections to become fluorescent during nerve
signaling (synaptic transmission).  They then exposed the flies to brief
puffs of an odor while they received a shock.  This caused them to learn
a new association between the odor and the shock ? a type of learning
called classical conditioning.

Using a high-powered microscope to watch the fluorescent signals in
flies brains with as they learned, the researchers discovered that a
specific set of neurons, called projection neurons, had a greater number
of active connections with other neurons after the conditioning
experiment.  These newly active connections appeared within 3 minutes
after the experiment, suggesting that the synapses which became active
after the learning took place were already formed but remained "silent"
until they were needed to represent the new memory.  The new synaptic
activity disappeared by 7 minutes after the experiment, but the flies
continued to avoid the odor they associated with the shock.  

This is the first time that optical imaging has been used to visualize a
memory trace, Dr. Davis says. "Its phenomenally powerful, like a movie
appearing in front of you," he adds.  The study suggests that the
earliest representation of a new memory occurs by rapid changes ? "like
flipping a switch" ? in the number of neuronal connections that respond
to the odor, rather than by formation of new connections or by an
increase in the number of neurons that represent an odor, he adds. 

The fact that the flies continued to show a learned response even after
the new synaptic activity waned suggests that other memory traces found
at higher levels in the brain took over to encode the memory for a
longer period of time, Dr. Davis suggests.  If so, the rapid changes of
nerve transmission that the researchers saw may be the all-important
switch that initiates the formation of new memories.  

This research suggests a previously unknown mechanism for how memories
are formed, Dr. Davis says.  While this study looked only at learning
related to odors, this newly identified process may be at work in many
other kinds of learning as well.  It is likely that these or similar
mechanisms are important for memory in humans and other animals, he
adds. 

"This is a remarkable study which uses molecular genetic approaches to
visualize memory formation in a living organism.  It demonstrates that,
in this model system, short term memory involves the recruitment of new
synaptic connections into pre-existing ensembles of synapses.  It will
be critical to determine whether similar principles control memory
formation in higher organisms," says Robert Finkelstein, Ph.D a program
director at NINDS.

The researchers now plan to put fluorescent genes into a variety of
other neurons of the brain in order to determine which ones respond to
different kinds of stimuli.  This will allow them to learn how the
changes they identified affect higher-level neurons. They also hope to
begin studying similar mechanisms in other animal models, such as mice.

The NINDS is a component of the National Institutes of Health within the
Department of Health and Human Services and is the nation's primary
supporter of biomedical research on the brain and nervous system.

1Yu D, Ponomarev A, Davis RL.  "Altered representation of the spatial
code for odors after olfactory classical conditioning:  memory trace
formation by synaptic recruitment."  Neuron, May 13, 2004, Vol. 42, No.
3, pp. 437?449.

Reviewed May 12, 2004

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