Adult Brain Cells Do Keep Growing

[Guest guest]

http://news./s/space/20051227/sc_space/adultbraincellsdokeep

growing;_ylt=AsLbdHMcdNr6ArtbtzY8XH2s0NUE;_ylu=X3oDMTA3MzV0MTdmBHNlYw

M3NTM-

Adult Brain Cells Do Keep Growing

Ker Than

LiveScience Staff Writer

LiveScience.com

Tue Dec 27, 4:00 PM ET

The apocryphal tale that you can't grow new brain cells just isn't

true. Neurons continue to grow and change beyond the first years of

development and well into adulthood, according to a new study.

The finding challenges the traditional belief that adult brain

cells, or neurons, are largely static and unable to change their

structures in response to new experiences.

The study, performed in adult mice, found that the branch-like

projections on some neurons, called " dendrites, " were still

physically malleable. Dendrites conduct electrical signals received

from other neurons to the parent neuron's cell body. The changes

occurred both incrementally and in short bursts, and involved both

growth and shrinkage.

Growth spurts

Some of the changes were dramatic by neuron standards. One dendrite

sprouted an impressive 90 microns (about .003 inches), more than

doubling its length in less than two weeks.

" The scale of change is much smaller than what goes on during the

critical period of development, but the fact that it goes on at all

is earth-shattering, " said study co-author Elly Nedivi, a

neuroscientists at the Massachusetts Institute of Technology (MIT).

During the early years following birth, humans manufacture an

estimated 250,000 neurons per minute and then spend the next few

years wiring them together. Traditionally, it was assumed that this

neural plasticity settles down by adulthood.

Neuroscientists have known for decades that adult neurons can change

their firing pattern and responses when faced with new experiences,

but whether they could change their structures remained an open

question.

The researchers observed the part of the brain responsible for

vision, called the visual cortex, over the course of a few months.

In order to see directly into the brain, the researchers implanted

glass windows over two areas of the visual cortex while the mice

were still young.

Looking in the wrong places

Neurons communicate with one another by exchanging either electrical

or chemical signals across tiny gaps where two neurons meet, called

synapses. The signals can be either excitatory or inhibitory,

meaning they either increase or decrease, respectively, the activity

of the neuron they're affecting.

Other studies looking into adult neuron growth focused mainly on

excitatory pyramidal neurons, but the MIT study examined other

neuron types as well. The researchers found that while pyramidal

neurons didn't exhibit any structural changes—which is consistent

with previous reports—a group of inhibitory neurons

called " interneurons " did.

The researchers estimate that on average, about 14 percent of the

interneurons they observed showed structural modifications.

Approximately 20 to 30 percent of the neurons in the neocortex, the

part of the brain responsible for higher functions such as thought,

are made up of inhibitory interneurons. These neurons are believed

to play an important role in regulating brain activity by delaying

or blocking signals from excitatory neurons.

The researchers speculated whether interneurons might be largely

responsible for neural plasticity in adult brains.

" Maybe the inhibitory network is where the capacity is for large-

scale changes, " Nedivi said.

The study, led by Wei-Chung Lee of MIT, was detailed in the

Dec. 27 issue of the journal for the Public Library of Science

(PLOS) Biology.