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Neuronal Diversity Makes a Difference, Research Finds
http://www.sciencedaily.com/releases/2010/08/100829202002.htm
ScienceDaily (Aug. 31, 2010) — Much like snowflakes, no two neurons
are exactly alike. But it's not the size or shape that sets one neuron
apart from another, it's the way it responds to incoming stimuli.
Carnegie Mellon University researchers have discovered that this
diversity is critical to overall brain function and essential in how
neurons process complex stimuli and code information.
The researchers published their findings, the first to examine the
function of neuron diversity, online in Nature Neuroscience.
"I think neuroscientists have, at an intuitive level, recognized the
variability between neurons, but we swept it under the rug because we
didn't consider that diversity could be a feature. Rather, we looked
at it as a fundamental reflection of the imprecision of biology," said
Nathan N. Urban, professor and head of CMU's Department of Biological
Sciences. "We wanted to reconsider that notion. Perhaps this diversity
is important -- maybe it serves some function."
Estimates say that the human brain alone has upwards of 100 billion
neurons, which can be broken down into a number of different types.
While members of the same type look structurally alike, and, as a
group, contribute to completing the same overall task, each individual
neuron in that group fires in response to subtle differences in the
incoming stimulus. Typically neuroscientists average out this
heterogeneity to obtain their results, assuming that the variability
is a "bug of biology."
"When we think about computer chips, variability in hardware clearly
can be very destructive. Manufacturers spend a lot of time and expense
making sure each processor on a chip is identical," Urban said. "The
brain is considered to be one of the most sophisticated computers
there is. We were intrigued by the idea that the brain might make use
of the messy, complex nature of its biological hardware to function
more efficiently."
Urban and postdoctoral student Krishnan Padmanabhan, both researchers
in CMU's Department of Biological Sciences and the joint
CMU/University of Pittsburgh Center for the Neural Basis of Cognition,
tested single neurons' responses to a complex stimulus. By placing an
electrical probe into individual excitatory neurons called mitral
cells and exposing them to a complex computer-controlled noise
stimulus, the researchers were able to determine how each cell
responded. They found that out of the dozens of neurons they tested,
no two had the exact same response. While the researchers believed
that these results were striking on their own, it led them to wonder
whether or not the neurons were giving a messy version of a single
response, or if they were each providing different pieces of
information about the stimulus.
To test their hypothesis, the CMU researchers used a tool called
spike-triggered averaging that allowed them to determine what feature
of the stimulus causes each neuron to respond. They found that some
responded to rapid changes in the stimulus and others to slower
changes; still other neurons responded when the input signal changed
in a regular or rhythmic way. The researchers then computed the
information contained in the outputs of highly diverse sets of neurons
and compared it to that of groups of more similar neurons. They found
that the heterogeneous groups of neurons transmitted two times as much
information about the stimulus than the homogeneous group.
"Diversity is an intrinsic good," Urban said. "A population in which
each member is a little different in terms of what they can do is a
more efficient and more effective population. It's like a baseball
team -- if you want to win, you shouldn't put nine pitchers on the
field."
Aside from its role in information coding, the researchers believe
neuronal diversity also could play a role in neurological disorders
like epilepsy, Parkinson's disease and schizophrenia. In these
conditions, there is a disruption in the synchrony and rhythmicity of
neuronal firing. In the case of epilepsy and Parkinson's, groups of
neurons fire simultaneously, causing seizures or tremors. In
schizophrenia, some neurons have a reduced ability to coordinate
firing in certain situations, such as during attention tasks. Changes
in the diversity of neuronal populations may alter the ease with which
neurons enter into these rhythmic firing patterns.
Additionally, the researchers want to discover how diversity is
achieved. Neurons of a given type are typically born at the same stage
of development, with many of them coming from the same progenitor
cell. Urban hopes to discover how neurons diversify during
development, what proteins are involved and if any type of training or
exposure enhances diversity.
This research was funded by the National Institute on Deafness and
Other Communication Disorders, one of the National Institutes of
Health.
Story Source:
The above story is reprinted (with editorial adaptations by
ScienceDaily staff) from materials provided by Carnegie Mellon
University, via EurekAlert!, a service of AAAS.
Journal Reference:
1. Krishnan Padmanabhan, Nathaniel N Urban. Intrinsic biophysical
diversity decorrelates neuronal firing while increasing information
content. Nature Neuroscience, 2010; DOI: 10.1038/nn.2630
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"Ethics" is simply a last-gasp attempt by deist conservatives and
orthodox dogmatics to keep humanity in ignorance and obscurantism,
through the well tried fermentation of fear, the fear of science and
new technologies.
There is nothing glorious about what our ancestors call history,
it is simply a succession of mistakes, intolerances and violations.
On the contrary, let us embrace Science and the new technologies
unfettered, for it is these which will liberate mankind from the
myth of god, and free us from our age old fears, from disease,
death and the sweat of labour.
Rael
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