Sensory deprivation affects brain's nerve connections

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Sensory deprivation affects brain's nerve connections

14 Jul 2005 Medical News Today

Scientists at New York University School of Medicine reveal the

important role of early experience in shaping neuronal development

and brain plasticity in a new study published in the July 14 issue of

the journal Nature.

In mice, the researchers found that sensory deprivation prevented the

substantial loss of synapses that typically occurs in growing

animals. The effects were most pronounced in the period from young

adolescence to adulthood. Synapses are the gaps between neurons

through which information travels.

Wen-Biao Gan, Ph.D., Assistant Professor of Physiology and

Neuroscience, and his colleagues captured images of brain plasticity--

its ability to adapt quickly to ever-changing circumstances--and have

started to unravel how this dynamic unfolds. The scientists were able

to deliver visible evidence of the effect of sensory deprivation.

It is well known that a growing child learns many skills. " What is

less known, " says Dr. Gan, " is that during childhood until puberty in

the human brain, as well as in the monkey and mouse, you see a

substantial loss of neuronal connections. " In learning, it appears

the brain needs to lose as it gains. He believes this loss may well

be the fundamental process underlying the development and plasticity

of the brain.

After birth, the number of synapses increases and then decreases

sharply. From early childhood to adolescence the synaptic loss could

be as much as 50 percent.

Dr. Gan believes that in order for learning to occur, the brain's

neurons have to be pruned. " First there is a raw material, and then

it is sculpted, " he says. In other words, learning isn't only about

making new connections between neurons, he says, it also involves

carving neuronal connections.

The authors of the new study are Yi Zuo, Guang Yang, Elaine Kwon, and

Dr. Gan of the Molecular Neurobiology Program at the Skirball

Institute of Biomolecular Medicine at NYU School of Medicine.

To get a glimpse of living neurons in mice, the researchers employed

a laborious technique for shaving the skulls of the animals. This

creates an ultrathin window on the brain through which one can peer

using a sophisticated optical technique called two-photon

fluorescence microscopy. Dr. Gan looked at dendritic spines, which

are thorny nubs found all along the branches of neurons. Spines,

which are continuously formed and eliminated, are where synapses are

made.

Since mice use their whiskers to explore their world, Dr. Gan altered

their experience by trimming the whiskers for two weeks on one side

of the mice's snouts. The spines of these mice were then compared to

spines in mice of the same age with untrimmed whiskers. Young mice

who kept their whiskers showed more spine loss than their whisker-

trimmed litter-mates.

In the adult age group, whisker trimming for two weeks appeared to

have no significant effect on spine loss. When the sensory

deprivation continued for two months, however, spine loss was

slightly reduced in adult animals as well. The scientists therefore

found that the period of young adolescence to adulthood was

particularly susceptible to sensory deprivation.

Interestingly, in adolescent mice the effects of sensory deprivation

on spine loss could be largely reversed if whiskers were allowed to

re-grow during a subsequent recovery period, says Dr. Gan. However,

the effects of sensory deprivation in young adolescence couldn't be

reversed if sensory recovery occurred after the mice reached

adulthood. These findings suggest " that childhood experience has a

long lasting and perhaps permanent impact on later life, " he says.

http://www.med.nyu.edu