>Pat
>
>>>>> Wait: neural paths aren't waves.
>
>right observation
>
>
>( from relative ignorance - this is not my direct field so I don't
>have the literature at hand darn)
>and following up on an earlier post which said there are no brainwaves (01)
The waves are revealed in EEGs, which are instruments which measure
electrical potentials on the surface of the scalp. I believe it is
known that these are in fact induced by a global preponderance of
neural activity in the cortex, but the EEG is a very coarse view of
the actual activity of the brain itself. (for one thing, there is a
bony skull between the brain and the skin.) More recent techniques,
notably MRI scanners, can 'see' regions of increased neural activity
in 3-D inside the actual brain, but what they detect directly is the
increased oxygen use from the blood supply to the brain, which is (a)
fairly coarse: it only gets you to the nearest 1000 neurons or so;
and (b) somewhat delayed, being about a second after the actual
neural event. Nevertheless, it shows very localized patterns of
neural activity in many circumstances. With nonhuman subjects (cats,
monkeys, mice), direct readings can be taken from fine needle
electrodes inserted into individual neurones, and most of the
detailed knowledge of functional brain anatomy has been discovered
this way, eg the visual cortex's arrangement into columns. As this
technique usually (though not always) involves killing the animal,
its not encouraged on human subjects. (02)
>
>I guess it depends on 'classification'
>
>(ontology for the brain link?) (03)
link? An ontology for all of brain science would be huge. I would
have no idea how to even start such a giant project. (04)
>
>brain activity
>frequency
>signal
>wave
>neural path
>other motion that can be detected?
>
>define and establish the relationships between them
>then we talk again
>
>
>1) according to commonly cited classification (I studied psychology
>one year), there are brainwaves and they have also names
>(alpha, beta etc)
>http://www.web-us.com/brainwavesfunction.htm (05)
Right, those are the EEG-detected waves. (06)
>They have been studied to some extent, but the subject may be more
>interdisciplinary than research is prepared to stretch to (07)
There has been a great deal of work on them and they are very well
understood. They are used in clinical diagnostic medicine, for
example. In fact, the local university here has one of the leading
labs in this area, which involves using very special equipment,
highly electrically screened to pick up very small changes in the
potentials. One needs a special building to do it in. (08)
>(personal
>view)
>
>2) Again, I am working on something else now but
>here is the reasoning
>
>>get definition and measurement (09)
I was presuming that you were referring to the 'paths' formed by the
synaptic connections between neurones. This is a well-defined notion.
Im not sure what you mean by 'measurement' though. (010)
>for 'neural path' (my springerlink is
>not responding)
>>>compare with definition and measurement for for brainwave as above
>>>> establish correlation, if any (011)
There isn't any. For one thing, the whole cortex seems to be quite
closely connected in the synaptic-path sense: every neuron (there are
about 14 trillion of them, far more than the number of people on
earth) is only about 7 synaptic links from every other neuron, on
average. But the EEG 'waves' pass through this connected network in
fairly regular rhythms, which are much slower than single neuron
firings. Heres an analogy: a huge crowd or people all talking to one
another and moving about. For some reason, when you watch this crowd
from high above, you can see that some of them are pointing in the
same direction, and at any given moment there is a preponderance of
people all looking north, say, forming a kind of vague 'stripe' in
the crowd, and that this 'stripe' (which you will call a
direction-wave) moves through the crowd slowly and regularly. At one
time, all the people *there* are looking north, then a bit later all
the people *there* (slightly to the south of the first place) are
looking north, and so on. The people don't move south, but the
preponderance of north-lookers "moves" in a southerly direction, like
a wave passing through the ocean. You can time it, in fact, and draw
a graph of it, and it seems to have a definite 'beat', with a
definite frequency, which is much slower than the rate at which the
people themselves move and talk. Nobody really knows why this
happens, but it often does. EEG waves are like that. (012)
>My entire speculative and relative ignorant guess is that the wave is
>a spatial representation of
>some electrical signal (013)
More like an aggregate of a very, very large number of signals, which
are in fact electrochemical rather than electrical. (Neural signals
operate by a 'wave' of sodium and potassium ion transfer through the
cell membrane; synaptic connections are done by the release of
chemicals called neurotransmitters, of which there are a large
number. Antidepressant drugs often work by stimulating the creation
of more neurotransmitter.) The electrical part of this is very weak
electricity, nothing like an electrical machine like a computer.
There is no way a brain could generate enough of an electrical field
to be picked up at a distance, in case you were wondering about that. (014)
Nobody really knows what the alpha and beta EEG rhythms are for.
There are several ideas about it which sound plausible, but nobody
has any way to test them directly. (015)
Pat (016)
>
>correct me please
>pdm
>
>
>On Dec 18, 2007 2:28 PM, Pat Hayes <phayes@xxxxxxx> wrote:
>> >On Dec 18, 2007 7:57 AM, Pat Hayes <phayes@xxxxxxx> wrote:
>> >
>> >> . Even if one were given a complete
>> >> (dead) mammalian brain, there is no conceivable
>> >> way to reconstruct all the neural connections in
>> >> it, since the total cross-section of a neuron's
>> >> end branchings greatly exceeds that of its axon,
>> >> and these neurons are tightly packed in the
>> >> cortex. Any way to 'take it apart' to find all
>> >> the neurons, therefore, would of necessity
>> >> involve breaking the connections which hold them
>> >> together. Put another way: its impossible to
>> >> assemble (or disassemble) a brain; it has to be
>> >> grown.
>> >
>> >This is precisely why I think the brain should be studied as a whole, and
>> >not in its puree or minced form.
>>
>> Well, everyone agrees with that, of course. The
>> problem is knowing how to start describing a
>> whole brain. BTW, it is definitely known that
>> different parts (areas) of the brain perform
>> distinct functions, even though they mostly look
>> similar under a microscope.
>>
>> > Thats the only way the neural paths (folk. 'brainwave') can be observed,
>>
>> Wait: neural paths aren't waves. Waves are
>> rhythmic patterns of activity across the whole
>> brain, like movements in a flock of birds. These
>> are only a tiny fraction of the total brain
>> activity, though, most of which seems to not be
>> 'waves' at all, more like flashes or bursts.
>>
>> >
>> >I hate to think like Frankenstein , but I bet you can induce some
>> >level of passive activity in a coma brain by passing some tiny
>> >frequencies.
>>
>> You can stimulate neurons in an awake brain by
>> small electrical impulses along a needle. The
>> person in the brain experiences some very odd
>> stuff, depending on where you do this to.
>>
>> > (not ac/dc I guess)
>> >I ll have to remember to do that experiment next time I come across a coma
>>
>> Well, speaking as an ex-epileptic, I'd rather you didn't.
>>
>> Pat :-)
>>
>> >
>> ><grin>
>> >
>> >PDM
>> >
>> >>
>> >>
>> >
>> >
>> >
>> >--
>> >Paola Di Maio
>> >School of IT
>> >www.mfu.ac.th
>> >*********************************************
>> >
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>>
>>
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>>
>
>
>
>--
>Paola Di Maio
>School of IT
>www.mfu.ac.th
>********************************************* (017)
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