 Study
shows new brain connections form rapidly during motor learning
SANTA CRUZ, CA--New connections
begin to form between brain cells almost immediately as animals
learn a new task, according to a study published this week in
Nature. Led by researchers at the University of California,
Santa Cruz, the study involved detailed observations of the
rewiring processes that take place in the brain during motor
learning.
The researchers studied mice as
they were trained to reach through a slot to get a seed. They
observed rapid growth of structures that form connections
(called synapses) between nerve cells in the motor cortex, the
brain layer that controls muscle movements.
"We found very quick and robust
synapse formation almost immediately, within one hour of the
start of training," said Yi Zuo, assistant professor of
molecular, cell and developmental biology at UCSC.
Zuo's team observed the formation
of structures called "dendritic spines" that grow on pyramidal
neurons in the motor cortex. The dendritic spines form synapses
with other nerve cells. At those synapses, the pyramidal neurons
receive input from other brain regions involved in motor
memories and muscle movements. The researchers found that growth
of new dendritic spines was followed by selective elimination of
pre-existing spines, so that the overall density of spines
returned to the original level.
"It's a remodeling process in
which the synapses that form during learning become
consolidated, while other synapses are lost," Zuo said. "Motor
learning makes a permanent mark in the brain. When you learn to
ride a bicycle, once the motor memory is formed, you don't
forget. The same is true when a mouse learns a new motor skill;
the animal learns how to do it and never forgets."
Understanding the basis for such
long-lasting memories is an important goal for neuroscientists,
with implications for efforts to help patients recover abilities
lost due to stroke or other injuries.
"We initiated the motor learning
studies to understand the process that takes place after a
stroke, when patients have to relearn how to do certain things.
We want to find out if there are things we can do to speed up
the recovery process," Zuo said.
The lead authors of the Nature
paper, Tonghui Xu and Xinzhu Yu, are a postdoctoral researcher
and doctoral student, respectively, in Zuo's lab at UCSC.
Coauthors include Andrew Perlik, Willie Tobin, and Jonathan
Zweig of UCSC and Kelly Tennant and Theresa Jones of the
University of Texas, Austin.
The study used mice that had been
genetically altered to make a fluorescent protein within certain
neurons in the brain. The researchers were then able to use a
special microscopy technique (two-photon microscopy) to obtain
clear images of those neurons near the surface of the brain. The
noninvasive imaging technique enabled them to view changes in
individual brain cells of the mice before, during, and after the
mice were trained in the seed-reaching task.
"We were able to follow the same
synapses over time, which had not been done before in a motor
learning study," Zuo said. "We showed that structural changes
occur in the brain at a much earlier stage than people had
believed."
Results from the study suggested
that the newly formed dendritic spines are initially unstable
and undergo a prolonged selection process during the course of
training before being converted into stable synapses.
When previously trained mice were
reintroduced to the reaching task four months later, their skill
at the task remained high, and images of their brains did not
show increased spine formation. When previously trained mice
were taught a new skill, however, they showed enhanced spine
formation and elimination similar to that seen during the
initial training. Furthermore, spines that had formed during the
initial training persisted after the remodeling process that
accompanied the learning of a new task.
These findings suggest that
different motor behaviors are stored using different sets of
synapses in the brain, Zuo said. One of the questions she would
like to explore in future studies is how these findings apply to
different types of learning.
"In China, where I grew up, we
memorize a lot in school. What are the changes that take place
in the brain during learning and memorizing, and what are the
best ways to consolidate those memories? We don't really know
the best way to learn and memorize," she said.
Contact: Tim Stephens
stephens@ucsc.edu
831-459-2495
University of
California - Santa Cruz
Source:Eurekalert
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