Lifelong memories linked to stable nerve connections

Dec 03, 2009
A small fraction of newly-formed spines persists. a-b, Repeated imaging of dendritic branches in the barrel cortex under a standard laboratory housing environment (a) and an enriched environment (b). Filled arrowheads indicate new spines that were formed during the first 2 days, and open arrowheads indicate spines existing on day 0 and eliminated over next 7 days. Scale bar, 2 µm. Credit: NYU Langone Medical Center

Our ability to learn new information and adapt to changes in our daily environment, as well as to retain lifelong memories, appears to lie in the minute junctions where nerve cells communicate, according to a new study by NYU Langone Medicine Center researchers. The study is published online this week in the journal Nature.

The scientists, led by Wen-Biao Gan, PhD, associate professor of physiology and neuroscience at NYU School of Medicine, discovered that a delicate balancing act occurs in the brain where neuronal connections are continually being formed, eliminated, and maintained. This feat allows the brain to integrate new information without jeopardizing already established memories, the new study suggests.

Using a powerful technique called two-photon microscopy, Dr. Gan and colleagues at The Helen and Martin Kimmel Center for Biology and Medicine at the Skirball Institute of Biomolecular Medicine, viewed the precise changes that take place at synapses, the junctions where nerve cells communicate, in the wake of learning a new task or being exposed to a novel situation. New knowledge, explains Dr. Gan, prompts alterations in the dendritic spines, the knobby protrusions along the branching ends of . With learning, spines are gained and others lost.

"We've known for a long time that the brain remodels after learning," says Dr. Gan "Our studies show that the brain does this in two ways: by adding a tiny fraction of new connections to the brain's and eliminating old ones."

Dr. Gan and his associates tracked changes in the brains of mice before and after experiencing a new stimulus (a string of beads hung at different places along the cage) or learning a new task (running on an accelerated spinning wheel). To open a window to the brain, the team shaved away the skull over the animals' cortex in which the nerve dendrites were lit up by fluorescent proteins. Then, using a two-photon microscope, they snapped photos of the dendrites after the animals learned to stay on the running wheel or encountered the newly positioned beads. The team began photographing the mice when they were a month old and followed them through adulthood.

When the team compared the photos across the months, they observed new spines emerging in response to the beads' placement or learning to run on the wheel. They saw, too, that as the mice became improved at spinning the wheel, a minute fraction of new spines continued to persist. The researchers also noted that at the same time as these new and lasting spines were created, a corresponding number of older spines that had been formed early in the animals' development before the experiment began, disappeared.

Despite the rise and fall of , the animals' brain circuitry remained overwhelmingly secure. A mouse neuron can carry ten thousand spines on its dendrites. Over months, only tens of spines were either gained or lost on each nerve cell after exposure to new experience while the majority of existing spines are maintained.

The study gives a clue as to how it is possible for humans, who have hundreds of thousands of spines on one neuron, to live each day, constantly experiencing and learning new things, without losing existing memories. "The brain is a dynamic and stable organ," says Dr. Gan.

Source: New York University School of Medicine (news : web)

Explore further: Built for speed: paranodal junction assembly in high performance nerves

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.

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.

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 ...

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 ...

Why you remember names and ski slopes

Nov 21, 2007

When you meet your boss's husband, Harvey, at the office holiday party, then bump into him an hour later over the onion dip, will you remember his name? Yes, thanks to a nifty protein in your brain called kalirin-7.

Recommended for you

Damage to brain networks affects stroke recovery

Nov 21, 2014

(Medical Xpress)—Initial results of an innovative study may significantly change how some patients are evaluated after a stroke, according to researchers at Washington University School of Medicine in St. ...

Dopamine leaves its mark in brain scans

Nov 21, 2014

Researchers use functional magnetic resonance imaging (fMRI) to identify which areas of the brain are active during specific tasks. The method reveals areas of the brain, in which energy use and hence oxygen ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.