<Modern human brain. Image source: Univ. of Wisconsin-Madison Brain Collection.
* Scientists know that information travels between
brain cells along hairlike extensions called axons. For the first time,
researchers have found that axons don’t just transmit information –
they can turn the signal up or down with the right stimulation.
This finding may help scientists develop
treatments for psychiatric disorders such as depression and
schizophrenia in which it is thought that different parts of the brain
do not communicate correctly with each other.
“Until now, scientists have thought that in the brain’s cortex --
where most cognitive processes occur -- information was only processed
in the cell body,” said Raju Metherate, author of the study, associate
professor of neurobiology and behavior, and director of the Center for
Hearing Research at UC Irvine. “The result of our study suggests that
we must consider the axons as sites of information processing – and of
potential problems when things go wrong.”
This study appears online Aug. 19 in Nature Neuroscience.
Increasingly, studies are beginning to show that complex
information processing, and perhaps consciousness itself, may result
from coordinated activity among many parts of the brain connected by
bundles of long axons. Cognitive problems may occur when these areas
don’t communicate properly with each other.
Cognitive function occurs when millions of brain cells communicate
with each other at the same time. A brain cell has a network of
branches called dendrites through which it receives and processes
information from other cells. The body of the cell then relays the
processed information along an axon to a terminal that links to another
cell’s dendrites. At the terminal, chemicals called neurotransmitters
are released, allowing the information to enter the receiving cell.
Until now, scientists believed axons were just the wires between point
A and point B.
“Axons, we thought, were like wires in a radio conveying signals, but
we found that if you stimulate the axon, the signal can be altered,
like turning the volume knob on the radio,” Metherate said.
Originally, Metherate and his colleagues had hoped to confirm the
idea that the drug nicotine alters information that is processed in the
cell body or terminal. Puzzled by several negative tests, they
developed an experiment in which they could study the intervening axon.
In their experiment, they examined a section of mouse brain
associated with hearing that contained a brain cell with an axon
connecting to the cortex. Using nicotine, they stimulated the axon to
determine how it would affect a signal the brain cell sent to the
cortex. Without applying nicotine, about 35 percent of the messages
sent by the brain cell reached the cortex. But when nicotine was
applied to the axon, the success rate nearly doubled to about 70
percent.
“We looked for more conventional reasons why the response was
enhanced, but the evidence just kept pointing to the axon. Nicotine
activated the proteins that we think are on the axon,” Metherate said.
“This is a completely new idea about how the brain works.”
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