Study shows new brain connections form rapidly during motor learning

Nov 29, 2009 By Tim Stephens
As mice learned a new task, repeated imaging of the same neurons over one-day intervals showed remodeling of synapses, with new branches (dendritic spines) forming and others eliminated during training. Image credit: Xu et al.

(PhysOrg.com) -- 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 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 . 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 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.

Source: University of California - Santa Cruz (news : web)

Explore further: Neurons can be reprogrammed to switch the emotional association of a memory

add to favorites email to friend print save as pdf

Related Stories

Short-term stress can affect learning and memory

Mar 11, 2008

Short-term stress lasting as little as a few hours can impair brain-cell communication in areas associated with learning and memory, University of California, Irvine researchers have found.

The building blocks of memory

Aug 20, 2007

Learning new things, remembering past experiences and adapting to a changing environment - these abilities carried out by the brain are essential for day-to-day survival. This unique flexibility is in part ...

New understanding of basic units of memory

Sep 19, 2007

A molecular “recycling plant” permits nerve cells in the brain to carry out two seemingly contradictory functions – changeable enough to record new experiences, yet permanent enough to maintain these memories over time.

Hairstyle of a Neuron: From Hairy to Mushroom-Head

Mar 07, 2007

Synapses are essential for the brain's normal function: their absence or presence is tightly linked to the brain's ability to transfer, process, and store information. Synapses are thus constantly generated ...

Proteins anchor memories in our brain

Nov 21, 2006

A University of Utah study suggests that memories are held in our brains because certain proteins serve as anchors, holding other proteins in place to strengthen synapses, which are connections between nerve cells.

Location, location, location

Jul 10, 2008

Neuroscientists at Georgetown University Medical Center have solved a mystery that lies at the heart of human learning, and they say the solution may help explain some forms of mental retardation as well as provide clues ...

Recommended for you

Emotional adjustment following traumatic brain injury

Oct 24, 2014

Life after a traumatic brain injury resulting from a car accident, a bad fall or a neurodegenerative disease changes a person forever. But the injury doesn't solely affect the survivor – the lives of their spouse or partner ...

New ALS associated gene identified using innovative strategy

Oct 22, 2014

Using an innovative exome sequencing strategy, a team of international scientists led by John Landers, PhD, at the University of Massachusetts Medical School has shown that TUBA4A, the gene encoding the Tubulin Alpha 4A protein, ...

User comments : 0