A Theory of The Brain


by Pythagorean
Tags: brain, theory
Pythagorean
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#19
Oct17-09, 03:25 AM
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Quote Quote by apeiron View Post
But while you fix on what brains (and nervous systems generally) do - anticipate the world - it would also be useful to invest some time in social psychology. Read some Vygotsky in particular. The human mind is scaffolded by its use of language and this is responsible for the "higher powers" we associate with human level consciousness.
There was a language lecture in the Yale set (last one I watched, actually) and the lecturer brought home how fundamental language is in human psychology. Of course, I've heard it before and generally agreed with it from experience. It's hard to think about, store, or learn anything without language even when you do it internally.

My knee-jerk response was "oh god, language is so hard to code", but I'm definitely interested in the idea. That's more of a postdoc project than even a PhD project, and I'm only just thinking of Master's project for now. From what I've read so far, it's likely to draw on the firing-rate model.

And above all, avoid becoming bogged down in phenomenological questions about consciousness - the hard question, qualia, theatres and all that. This has killed mind science again and again.
Well, I don't suppose getting bogged down (at least not for the long-term) is likely to happen, but I definitely can't help but be very emotionally attached to phenomenological questions, and want to find solutions to answering them.

However, I think these things emerge in the strangest ways if we don't pay attention to them. I especially like Vilayanur Ramachandran's tangent on synethsesia and its connection to creativity... this would be worth investigating to me. If you haven't watched his video, I referenced it earlier in this thread and will do so for you again as I'm desperate to share discussion on it and want to make it as easy as I can for you to watch it in the hopes that you will:

http://www.youtube.com/watch?v=Rl2LwnaUA-k
apeiron
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#20
Oct17-09, 05:30 AM
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Quote Quote by Pythagorean View Post
I especially like Vilayanur Ramachandran's tangent on synethsesia and its connection to creativity... this would be worth investigating to me.
But what's the question exactly?

Under-pruning of synapses would be the standard speculative story on synesthesia. Stuff spills over. And conversely, a well-organised left fusiform gyrus would act as a "module" for orderly cross-modal tieing together (though perhaps more an evolutionary emphasis on language processing that any kind of human creativity module). But anyway, you have two kinds of neural story here - one of overly diffuse connection, the other of focused connectedness.

If anything, this would lead into a discussion of brain organisation as a set of dichotomies. So diffused~focused. Or plasticity~stability to pick a more telling dimension for neural net design.

Actual creative leaps are probably best modelled in threshold terms - competitive neural nets.

When the mind is fixed on one idea, it cannot see other possibilities. It is in a state of high neural contrast where something is very conscious - high firing rates, high synchrony - and all other memory traces literally suppressed. Low reactivity. low synchrony.

So to jump to some other version of events, some other arrangement of stored knowledge, the mind has to relax. Go flat. Then competition can bring another pattern of connections to the fore. Forge a new link - this could be flipped round to now fit that.

This is why solutions often pop into mind when we are "looking the other way" - relaxed theta rhythm story, or check the priming literature.
Pythagorean
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Oct17-09, 05:42 AM
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Quote Quote by apeiron View Post
But what's the question exactly?

Under-pruning of synapses would be the standard speculative story on synesthesia. Stuff spills over. And conversely, a well-organised left fusiform gyrus would act as a "module" for orderly cross-modal tieing together (though perhaps more an evolutionary emphasis on language processing that any kind of human creativity module). But anyway, you have two kinds of neural story here - one of overly diffuse connection, the other of focused connectedness.
My natural assumption was that the connections found each other post-pruning when I first heard of synesthesia.

Anyhow, the question is not the thing here. The question is the thing for technical works to be produced. The thing here is the ambition, the curiosity. Questions poor out my ears. Eventually, I'll find one that both hasn't been answered yet and is within my reach to verify.
granpa
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#22
Oct17-09, 08:18 AM
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regarding synethsesia:
blue=colorized black
red=colorized grey
yellow=colorized white

green=blue+yellow
purple=blue+red
orange=red+yellow

are these examples of synethsesia?

how about these?
sour=sweet+bitter
salty=hot+cold

or these?
sweet=pleasure+taste
apeiron
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Oct17-09, 04:07 PM
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Quote Quote by granpa View Post
regarding synethsesia:
blue=colorized black
red=colorized grey
yellow=colorized white

green=blue+yellow
purple=blue+red
orange=red+yellow

are these examples of synethsesia?

This does not seem an accurate way to introspect about colour experience.

Green does not appear like a blue-yellow mixture but instead seems a pure colour experience.

On the other hand, you can have blackish blue, red and green (navy blue, crimson, forest green) yet not a blackish yellow. Instead you get brown from a low reflectance yellow.

Student demonstrated this with a chocolate bar viewed against a bright light backdrop. The brown turns yellow.

This is explained neurally by the fact we have three colour pigments but four colour opponent channels - so yellow is interpolated at a higher level of processing as a "primary" to counter blue. And the effect of relative brightness on colour experience.
Evo
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Oct17-09, 04:51 PM
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Quote Quote by granpa View Post
regarding synethsesia:
blue=colorized black
red=colorized grey
yellow=colorized white

green=blue+yellow
purple=blue+red
orange=red+yellow

are these examples of synethsesia?

how about these?
sour=sweet+bitter
salty=hot+cold

or these?
sweet=pleasure+taste
No, these wouldn't be examples.

My older daughter is a synesthete and see numbers as colors. A synesthete might "hear" colors. They might "taste" numbers. A flavor might feel "pointed or sharp"
granpa
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#25
Oct17-09, 05:34 PM
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Quote Quote by Evo View Post
No, these wouldn't be examples.

My older daughter is a synesthete and see numbers as colors. A synesthete might "hear" colors. They might "taste" numbers. A flavor might feel "pointed or sharp"
sweet=pleasure+taste?
granpa
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#26
Oct17-09, 05:52 PM
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Moreover, my point (yes there was a point) was that maybe these things evolved by first passing through a stage a synethsesia. today we would say that purple is not red or blue but a separate color. yet even now I can kinda see purple as being sorta bluish in a way and at the same time sorta redish in a way.
cesiumfrog
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#27
Oct17-09, 06:14 PM
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Quote Quote by granpa View Post
Moreover, my point (yes there was a point) was that maybe these things evolved by first passing through a stage a synethsesia. today we would say that purple is not red or blue but a separate color. yet even now I can kinda see purple as being sorta bluish in a way and at the same time sorta redish in a way.
Purple is reddish blue, but normally there is no such thing as bluish yellow. So I don't see quite what you're getting at..
apeiron
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Oct17-09, 06:23 PM
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Quote Quote by granpa View Post
Moreover, my point (yes there was a point) was that maybe these things evolved by first passing through a stage a synethsesia. today we would say that purple is not red or blue but a separate color. yet even now I can kinda see purple as being sorta bluish in a way and at the same time sorta redish in a way.
Synesthesia as a condition is defined by cross-modal binding of perceptual experiences. But we could generalise the neural lessons to point out how neurons code as much for "not this" as "yes, that". That is, they code with a dichotomous logic.

So a retinal ganglion cell is wired to have an “on/off” receptive field. It compares excitatory input from one type of cone cell, say red, with the inhibitory input from a surround of opponent cells, which would be green. It would then fire strongly when it "saw" red surrounded by not-green. And alternatively, would have its baseline firing rate suppressed, desynchronised, when it saw not-red and surrounding green.

Red and green are of course misleading terms at this level of description as the red cone is broadly tuned - it shows a bell curve response to wavelength that simply peaks at a particular frequency. So will show some response to bright enough "green".

Anyway, a general principle of neural circuitry is that local responses are shaped by global contextual effects. It is all about the cross-wiring. And synthesia is just the cross-wiring being extended too promiscuously across cortical areas. Seeing yellow ought to trigger experiences of not-number and not-shape. Because the yellow object might be actually just a banana or a coloured test card,

And so the cross-wiring should be binding cross-modally to these actual memories - our banana recognition circuitry should be going yes-banana-like and yes-yellow. And so not-cat and not-apple (other objects), and not-blue, not-black (other colours, unless it is a very old banana).

Synthesia is a failure to suppress contextual associations. Note that the reaction is to fairly specific and high-level stimuli - number names and words and musical notes. Quite sharply localised. And from that would seem to be part of the human brain's tinkering to handle language. Evolution had to jiggle with cross-modal connectedness so that words triggered the right learnt penumbra of associative response - hearing banana did result in not-black, yes-yellow, etc.
apeiron
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#29
Oct17-09, 06:32 PM
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Quote Quote by cesiumfrog View Post
Purple is reddish blue, but normally there is no such thing as bluish yellow. So I don't see quite what you're getting at..
Red and blue are not opponent colours, yet blue and yellow are. Which is why red and blue can look mixed, but blue and yellow resist and want to be seen only as pure green.

Likewise red and green are opponent so resist being seen as mixed, but you can have greeny blue or greeny yellow.

Look at the wiring of the visual pathway and these qualitative aspects of experience make quantitative sense (though there is still admittedly the qualitative "hard problem" of why green is "greenish", even if we know it is the brain saying we are seeing not-red).
Evo
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Oct17-09, 06:55 PM
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This is a very good basic explanation of synesthesia.

What is synesthesia?
Synesthesia is a condition in which one sense (for example, hearing) is simultaneously perceived as if by one or more additional senses such as sight. Another form of synesthesia joins objects such as letters, shapes, numbers or people's names with a sensory perception such as smell, color or flavor. The word synesthesia comes from two Greek words, syn (together) and aisthesis (perception). Therefore, synesthesia literally means "joined perception."

Synesthesia can involve any of the senses. The most common form, colored letters and numbers, occurs when someone always sees a certain color in response to a certain letter of the alphabet or number. For example, a synesthete (a person with synesthesia) might see the word "plane" as mint green or the number "4" as dark brown. There are also synesthetes who hear sounds in response to smell, who smell in response to touch, or who feel something in response to sight. Just about any combination of the senses is possible

The Biological Basis of Synesthesia
Some scientists believe that synesthesia results from "crossed-wiring" in the brain. They hypothesize that in synesthetes, neurons and synapses that are "supposed" to be contained within one sensory system cross to another sensory system. It is unclear why this might happen but some researchers believe that these crossed connections are present in everyone at birth, and only later are the connections refined. In some studies, infants respond to sensory stimuli in a way that researchers think may involve synesthetic perceptions. It is hypothesized by these researchers that many children have crossed connections and later lose them. Adult synesthetes may have simply retained these crossed connections.

It is unclear which parts of the brain are involved in synesthesia. Richard Cytowic's research has led him to believe that the limbic system is primarily responsible for synesthetic experiences. The limbic system includes several brain structures primarily responsible for regulating our emotional responses. Other research, however, has shown significant activity in the cerebral cortex during synesthetic experiences. In fact, studies have shown a particularly interesting effect in the cortex: colored-hearing synesthetes have been shown to display activity in several areas of the visual cortex when they hear certain words. In particular, areas of the visual cortex associated with processing color are activated when the synesthetes hear words. Non-synesthetes do not show activity in these areas, even when asked to imagine colors or to associate certain colors with certain words.
And for pythagorean
Synesthesia and the Study of Consciousness
Many researchers are interested in synesthesia because it may reveal something about human consciousness. One of the biggest mysteries in the study of consciousness is what is called the "binding problem." No one knows how we bind all of our perceptions together into one complete whole. For example, when you hold a flower, you see the colors, you see its shape, you smell its scent, and you feel its texture. Your brain manages to bind all of these perceptions together into one concept of a flower. Synesthetes might have additional perceptions that add to their concept of a flower. Studying these perceptions may someday help us understand how we perceive our world.
http://faculty.washington.edu/chudler/syne.html
Pythagorean
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#31
Oct17-09, 08:57 PM
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Quote Quote by Evo View Post
I've just heard about the binding problem and been thinking about it, specifically with respect to how it makes the conscious part of vision a very abstract representation of the real world (highly efficient, dude to it's weighing of importance. By conscious part of vision, I mean that which we interpret which we see. This is opposed to the unconscious part of vision (which can be somewhat isolated in patients with "blind sight"). The patient is aware of kinematic changes in his vision (actually... is he actively aware or does he have to recall it from short-term memory if he chooses to think about it?) but doesn't interpret them "visually" by the standard definition of visual.

So I think the binding problem goes beyond just the binding of senses, but also the binding of some kind of symbolic memory. For instance, you're in a room with a metal worker and a bunch of junk all over, but you're not really paying attention to the junk because you're talking to the metal-worker. It's all formless, even as it's in your field of vision. But as you begin to look at things, you identify the individual pieces of the junk, you know what they are from experience, and as you analyze each piece and identify it, your also relying on your memory to construct the details you can't directly sense. You can imagine how it would smell or feel or taste or sound based on experience.

Language itself seems to be a kind of way to reinforce symbolic memory, if it's not in some way directly responsible for it.
Galteeth
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#32
Oct18-09, 02:04 AM
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Quote Quote by apeiron View Post
Synesthesia as a condition is defined by cross-modal binding of perceptual experiences. But we could generalise the neural lessons to point out how neurons code as much for "not this" as "yes, that". That is, they code with a dichotomous logic.

So a retinal ganglion cell is wired to have an “on/off” receptive field. It compares excitatory input from one type of cone cell, say red, with the inhibitory input from a surround of opponent cells, which would be green. It would then fire strongly when it "saw" red surrounded by not-green. And alternatively, would have its baseline firing rate suppressed, desynchronised, when it saw not-red and surrounding green.

Red and green are of course misleading terms at this level of description as the red cone is broadly tuned - it shows a bell curve response to wavelength that simply peaks at a particular frequency. So will show some response to bright enough "green".

Anyway, a general principle of neural circuitry is that local responses are shaped by global contextual effects. It is all about the cross-wiring. And synthesia is just the cross-wiring being extended too promiscuously across cortical areas. Seeing yellow ought to trigger experiences of not-number and not-shape. Because the yellow object might be actually just a banana or a coloured test card,

And so the cross-wiring should be binding cross-modally to these actual memories - our banana recognition circuitry should be going yes-banana-like and yes-yellow. And so not-cat and not-apple (other objects), and not-blue, not-black (other colours, unless it is a very old banana).

Synthesia is a failure to suppress contextual associations. Note that the reaction is to fairly specific and high-level stimuli - number names and words and musical notes. Quite sharply localised. And from that would seem to be part of the human brain's tinkering to handle language. Evolution had to jiggle with cross-modal connectedness so that words triggered the right learnt penumbra of associative response - hearing banana did result in not-black, yes-yellow, etc.
I wonder if the same kind of suppression failure occurs in less specific and localised forms.

It is curious that schizophrenia, which seems to result from a lack of basic sensory filtering, produces a syndrome that makes higher level associations more difficult.

I suppose one is just context suppression failure whereas the other is a more basic suppression failure.


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