
Eyes see trouble coming before brain notices - soundsop
http://www.newscientist.com/article/dn17744-eyes-see-trouble-coming-before-brain-notices.html?DCMP=OTC-rss&nsref=online-news
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jacquesm
Reflexes are also interesting, apparently the round-trip time to the brain for
information is so long that in some situations something quicker is needed.

So, you could probably conclude that some thresholding, computation and
feedback capability is present in all neural tissue, including the spinal
cord.

Apparently an octopus has one 'main' brain and 8 'auxiliary' brains, one for
each of its tentacles.

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a-priori
Well, first of all octopi are invertebrates, so their nervous systems are
quite dramatically different from ours. If I remember right, an octopus' axons
are unmyelinated (I don't know much about invertebrates; I know some
invertebrates have myelination, but I don't think octopi do). This means that
it's quite a bit slower to transmit signals around in their bodies, so in
order to react quickly they need bundles of neurons near the sources of the
signals.

Perhaps as a throw-back to our invertebrate ancestors, we still have
unmyelinated fibres that transmit some kinds of information, such as some
forms of pain. That's why if you stub your toe, you feel two waves of pain:
one sharp and quick, and the other much duller. The second one travels over
unmyelinated fibres, and so takes much longer to arrive in your brain.

If all you had were unmyelinated fibres, and if control were centralized in
your brain, you'd have a round-trip time of a few seconds to your feet. How
could you control your legs for walking like this?

Obviously, we do have myelinated axons, so things are quicker, but it's still
impractical to involve the brain in most reactions, because it's large and
complex and takes a while to reach a steady-state after unexpected stimuli.

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jacquesm
Thank you, that was most interesting. I knew about the myelination (sp?), but
did not realize that that affected the speed of transmission so much.

Very interesting about the secondary system still being active, maybe that is
what allows us to measure the distance of a stimulus to the brain by using the
difference between the arrival times of the pulses ?

Are you working in this field ?

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a-priori
Yeah, myelination really is a huge improvement. According to Wikipedia [1],
the fast pain fibres I mentioned (A-delta) have a conduction speed of 3-30
m/s, and the slow fibres (C) have a speed of 0.5-2.0 m/s. As you can see on
that page, there are much faster fibres than those.

For some definition of "field", I suppose I do :) I did a minor in cognitive
neuropsychology in university, and now I'm doing an internship for a
computational neuroscience project.

[1]: <http://en.wikipedia.org/wiki/Axon#Types>

(Edit: I don't know why we still have slow "C" fibres. I suppose there's no
pressure to get rid of them, so they've just stuck around all this time. It
probably helps with learning, because it persists for a longer time, whereas
the fast signal is more for the immediate reaction... just a guess.)

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mkelly
I wonder these cells do when they detect an object approaching. Is this the
reflex for closing the eyelids, or something else?

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a-priori
This article doesn't get into the behavioural response to this, because
they're solely concerned with characterizing things at the cellular level.

Personally, I doubt this would cause the eyelids to close (stimulation of the
eyelashes already does this). It may activate the startle reflex, or perhaps
initiate a saccade to focus the eyes on the stimuli. More research will surely
follow to figure out exactly what behavioural role this information plays.

It's already known, for example, that cells in V1 (primary visual cortex)
respond to similar motion. Either the V1 cells receive input from these
ganglion cells, or their function is somehow complementary to this (a
different time scale, for example).

Also interesting, this new finding directly contradicts existing research: "It
is generally assumed that there is no sizable proportion of motion detectors
in the primate retina." (Bach and Hoffman, 1999;
<http://dx.doi.org/10.1016/S0042-6989(00)00106-1>)

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rw
Indicates that reverse-engineering human intelligence is harder than merely
understanding the brain.

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jonsen
I believe it's common to regard the eyes as extensions of the brain.

