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[News]: Spineless Tales Provide Strong Backbone to Human Brain Research - Newswise (press release)

octobot

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#1

monty

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Sounds like very interesting research prepared by a science writer with no grasp whatsoever of the work... I can't find the pre-release URL anywhere, so I guess I have to wait 'till the official publication :razz: In the meantime, I will make fun of the anonymous newswise reporter, however:

Color change in cuttlefish skin is caused by pigments in star-shaped cells known as chromatophores. Upon certain inputs, pigment granules spread outward in cells, causing human skin, for instance, to tan or a chameleon’s skin to turn between green and brown. However, such changes take hours in humans and minutes in lizards. Cephalopods have some two million chromatophores that are directed by chemical signals originating in a central brain location.
Um, humans don't have chromatophores at all... when human chromatophores are available, I want to be first in line! I don't remember how chameleons work, but I'm pretty sure they don't either. I think the reporter probably wrote that chromatophores contain a pigment similar to human melatonin, and is confused. Although in a huge stretch, all nerve signals are chemical, a fundamental element of the ceph color change system is that it's controlled directly by the nervous system, by nerves running from the brain to the muscles of the chromatophores, so there is nothing special about the chemistry at the chromatophore end. It sounds like what's interesting is the neurotransmitter chemistry in the cuttlefish brain in the region controlling the chromatophores.

I'm really interested in the homunculus they've mapped, and I'd be particularly interested in how it relates to the cuttlefish's visual map of the world.

Cephalopods, which also include octopuses and squids, have 100 million nerve cells compared to the 10,000 in insects and the some one trillion in humans.
Unless something has changed dramatically recently, the human brain has about 100 billion neurons, not one trillion. This link suggests that the figures aren't so hot for cephs or insects, either, although they're not of by a whole factor of ten:

http://faculty.washington.edu/chudler/facts.html#brain

Average number of neurons in the brain = 100 billion
Number of neurons in brain (octopus) = 300 million (from How Animals See, S. Sinclair, 1985)
I've seen other references cite 100-200 million for octopus before, too. Messenger and Young claim that O. Vulgaris has 2 x 10^5 (200 thousand) cells at birth and 2 x 10^8 (200 million) at adulthood of which about 129 million are in the optic lobes. They don't give a number for Sepia officinalis there is a table that compares the volumes of brains of cephs that puts O. vulgaris at 92.6 mm3 CNS and 79.0 mm3 optic lobes, which lists S. officinalis at 163.8 and 232.4. A little arithmetic: (163.8+232.4)/(92.6+79.0) = 2.3, so 460 million is a guess for an adult cuttlefish. (extra trivia: GPOs have bigger brains than Architeuthis if you don't count the optic lobes.)

Anyway, I applaud the octobot for finding an interesting article and ridicule the anonymous science reporter for being unable to articulate it... I'm looking forward to reading the real paper, though!
 

sorseress

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OOOO! I'd love to have chromatophores! I could be all flashy, like a fire opal (or a cuttlefish)!
 

OB

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#5
You flamboyant, you :wink:
 

OB

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#7
:lol:
 

Fujisawas Sake

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The homomunculus map (or ceph-unculus, I guess) would be interesting. Is there a way to run an EEG on a ceph though?

Another interesting thought is if there is any signal degradation with cephalopod action potentials along their giant axons. I still don't think myelin sheaths in vertebrates are just simply to acclerate AP's.
 

monty

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Fujisawas Sake;85431 said:
The homomunculus map (or ceph-unculus, I guess) would be interesting. Is there a way to run an EEG on a ceph though?

Another interesting thought is if there is any signal degradation with cephalopod action potentials along their giant axons. I still don't think myelin sheaths in vertebrates are just simply to acclerate AP's.
I can't think of any reason an EEG wouldn't work on a ceph, although their brains are somewhat "deeper inside" than vertebrates, so just sticking sensors on the head might not pick up stuff so well. Of course, the whole "immersed in conductive salt water" thing might be a bit odd, too.

A neat thing about axons, myelinated or otherwise, is that they are self-correcting so that there is zero degradation of the action potential, normally (unlike dendrites)-- each step in the cascade of propagation is essentially a "my neighbor crossed the threshold, so I'm going to do it, too"-- more like a wave of individuals standing up at a stadium event than an actual water wave that degrades over time-- if the guy next to you doesn't stand up all the way, it doesn't change whether you do on your own turn... similarly, once the membrane is depolarized (or is it hyperpolarized? I think it's hyperpolarized in its rest state) from the action potential "upstream," the opening of the voltage-gated Na and K channels do their dance and reproduce a perfect action potential at that local region on the axon, as long as the signal was enough to trigger it at all. If it wasn't enough for some reason, it doesn't trigger the action potential at all, but there's never (insofar as absolutes ever apply in biology) a partial action potential (unless some nasty neurobiologist or blue-ringed octopus has blocked the Na channels with TTX or something.)

With myelin, the action potential propagates passively between the gaps in the myelin, but otherwise works pretty much the same way...
 

Fujisawas Sake

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#11
sorseress;77390 said:
OOOO! I'd love to have chromatophores! I could be all flashy, like a fire opal (or a cuttlefish)!
Nah, I'd rather have nematocysts...

And sharks with FRICKIN' laser beams on their foreheads...

Oh! Oh! And flying attack porcupines....
 

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