On 28 Oct 2013, at 16:52, Craig Weinberg wrote:
http://medicalxpress.com/news/2013-10-neuroscientists-mini-neural-brain.html
Dendrites, the branch-like projections of neurons, were once thought
to be passive wiring in the brain. But now researchers at the
University of North Carolina at Chapel Hill have shown that these
dendrites do more than relay information from one neuron to the
next. They actively process information, multiplying the brain's
computing power.
"Suddenly, it's as if the processing power of the brain is much
greater than we had originally thought," said Spencer Smith, PhD, an
assistant professor in the UNC School of Medicine.
His team's findings, published October 27 in the journal Nature,
could change the way scientists think about long-standing scientific
models of how neural circuitry functions in the brain, while also
helping researchers better understand neurological disorders.
"Imagine you're reverse engineering a piece of alien technology, and
what you thought was simple wiring turns out to be transistors that
compute information," Smith said. "That's what this finding is like.
The implications are exciting to think about."
Axons are where neurons conventionally generate electrical spikes,
but many of the same molecules that support axonal spikes are also
present in the dendrites. Previous research using dissected brain
tissue had demonstrated that dendrites can use those molecules to
generate electrical spikes themselves, but it was unclear whether
normal brain activity involved those dendritic spikes. For example,
could dendritic spikes be involved in how we see?
The answer, Smith's team found, is yes. Dendrites effectively act as
mini-neural computers, actively processing neuronal input signals
themselves.
Directly demonstrating this required a series of intricate
experiments that took years and spanned two continents, beginning in
senior author Michael Hausser's lab at University College London,
and being completed after Smith and Ikuko Smith, PhD, DVM, set up
their own lab at the University of North Carolina. They used patch-
clamp electrophysiology to attach a microscopic glass pipette
electrode, filled with a physiological solution, to a neuronal
dendrite in the brain of a mouse. The idea was to directly "listen"
in on the electrical signaling process.
"Attaching the pipette to a dendrite is tremendously technically
challenging," Smith said. "You can't approach the dendrite from any
direction. And you can't see the dendrite. So you have to do this
blind. It's like fishing if all you can see is the electrical trace
of a fish." And you can't use bait. "You just go for it and see if
you can hit a dendrite," he said. "Most of the time you can't."
Once the pipette was attached to a dendrite, Smith's team took
electrical recordings from individual dendrites within the brains of
anesthetized and awake mice. As the mice viewed visual stimuli on a
computer screen, the researchers saw an unusual pattern of
electrical signals – bursts of spikes – in the dendrite.
Smith's team then found that the dendritic spikes occurred
selectively, depending on the visual stimulus, indicating that the
dendrites processed information about what the animal was seeing.
To provide visual evidence of their finding, Smith's team filled
neurons with calcium dye, which provided an optical readout of
spiking. This revealed that dendrites fired spikes while other parts
of the neuron did not, meaning that the spikes were the result of
local processing within the dendrites.
Study co-author Tiago Branco, PhD, created a biophysical,
mathematical model of neurons and found that known mechanisms could
support the dendritic spiking recorded electrically, further
validating the interpretation of the data.
"All the data pointed to the same conclusion," Smith said. "The
dendrites are not passive integrators of sensory-driven input; they
seem to be a computational unit as well."
His team plans to explore what this newly discovered dendritic role
may play in brain circuitry and particularly in conditions like
Timothy syndrome, in which the integration of dendritic signals may
go awry.
"This revealed that dendrites fired spikes while other parts of the
neuron did not, meaning that the spikes were the result of local
processing within the dendrites."
Yep, looks like neurons have a nervous system of their own now.
Still think that consciousness is a product of the brain?
I refer you to my rare posts where I suggest that the level is the
molecular level, and should include the glial cells, which in my
opinion (from diverse reading) handle to information.
I also defend the idea that an amoeba, by being unicellular, can be
seen as a cell being simultaneously a digestive cell, a muscular
cells, a liver cell, a kidney cell, a bone cell, and a brain cell.
Amoebas are not completely stupid and deserve respects, and so are any
each of our own cells, despite those cells in multicellular organism
have lost a bit of their freedom and universality to cooperate in what
is ourself.
Again, the bold quote illustrates comp, and the fact that the level is
lower than some thought.
Also with comp, consciousness is NOT a product of the mind. that's
still too much an aristotelian way to express the "identity" thesis.
Consciousness is not physical, it is the mental state of person
associated to machines, when those person develop *some* true belief.
Bruno
http://iridia.ulb.ac.be/~marchal/
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