UCSD Study Shows How We Perceive
On Precise Division Of Labor Among Cells In Brain
By Sherry Seethaler
California, San Diego neurobiologists have uncovered evidence
that sheds light on the long-standing mystery of how the brain
makes sense of the information contained in electrical impulses
sent to it by millions of neurons from the body.
In a paper published this week in the early on-line version
of the journal Nature, a UCSD team led by Massimo Scanziani
explains how neurons, or nerve cells, in the brain sort out
information before deciding how to respond. The paper will appear
in a forthcoming print issue of Nature.
shows individual specialized brain neurons in different
colors with brain slice in the background
Photo credit: Massimo Scanziani and
Frédéric Pouille, UCSD
Light, sound and odors,
for example, are transformed by our sensory organs into a code
made of series of electrical impulses that travel along neurons
from the body to the brain. Information about the onset and
the intensity of a stimulus is thought to be sent to the brain
by the timing and frequency of these electrical impulses. How
information is sorted by the brain has been an open question.
The group discovered that different neurons in the brain are
dedicated to respond to specific portions of the information.
“Our work shows that deciphering the enormous amount of
information that is conveyed to the brain at any time-point
is a matter of division of labor between specialized neurons,”
explains Scanziani, an assistant professor of biology. “Each
neuron literally ’picks’ the type information it
is supposed to process, that it is competent for. Very much
like each musician in an orchestra only reads that part of the
score of a symphony that was written for his or her own instrument.”
Because they needed
to see and record electrical impulses from individual nerve
cells, the researchers used slices of rat brain, which when
bathed in an appropriate solution can be kept alive under a
microscope. To mimic incoming information, the first author
on the paper, Frédéric Pouille, a postdoctoral
fellow in Scanziani’s laboratory, provided an electrical
stimulus—analogous to the score in Scanziani’s analogy—and
then monitored which nerve cell read which part of the information.
Pouille and Scanziani found some nerve cells that were only
responsive to the first impulse that arrived, while other nerve
cells only responded to multiple electrical impulses arriving
at certain frequencies.
“While some neurons only responded to the onset of each
package of information, which, in other words, means: Hey, something
just arrived, other neurons actually looked into the package
and played the notes,” says Scanziani.
Each of these specialized
brain neurons has a highly branched structure where many neurons
carrying sensory information can form connections. At any moment,
each of these specialized brain neurons might be receiving multiple
messages from multiple sources, but is only selectively responding
to certain information about the timing or frequency of the
impulses it is receiving.
Why is the timing of
information so important? Visual, tactile and auditory information
needs to be synchronized. If it were not, then one might, for
example, perceive someone’s lips move before hearing the
words being spoken—like a badly dubbed foreign film.
The brain also needs to know how intense a stimulus is because
intensity will influence what action needs to be taken. For
example, an uncomfortable shoe will become more and more difficult
to ignore as your foot develops a blister. As the blister develops,
the interval between subsequent electrical impulses arriving
at the brain would decrease; in other words, their frequency
would increase. Scanziani speculates that there might even be
an “alarm neuron” in the brain that responds to
high frequency electrical impulses by triggering the appropriate
muscle response to escape the stimulus.
“This study advances our understanding of how the brain
reads a code made of identical electrical impulses, in order
to produce a coherent perception of the world,” he says.
“Deciphering the language of the brain will help us understand
the neuronal basis for sensation and cognition and their associated
In their paper, the
UCSD researchers also determine a chain of physiological mechanisms
working in concert to allow these brain neurons to selectively
respond to a specific pattern of incoming electrical impulses.
Communication across the connections between neurons is usually
chemical rather than electrical. The researchers found that
the differences in the way the individual brain neurons released
and responded to these chemicals could explain their differing
responses to incoming information.
Scanziani and Pouille’s
experiments focused on the hippocampus—a region of the
brain known to be important in learning in memory. But they
believe that other regions of the brain may also use the same
principles to sort information. However, the researchers point
out that brain slices are a simplified system, and more research
is needed before they will understand the finer details of this
“This is only part of the picture,” cautions Scanziani.
“We are not looking at the whole orchestra, maybe only
the violins and the oboes. But down the line we plan to look
at further classes of nerve cells.”
The research study
was initiated when Scanziani was an assistant professor at the
Brain Research Institute of the University of Zurich. The work
was supported by the National Institutes of Health and the Swiss
National Science Foundation.
Sherry Seethaler (858)
Comment: Massimo Scanziani