20131003_Class 2_Ch 2 PDF 文件
•"MRI"？
–M (magnetic): 訊號的來源，人體中小磁鐵的磁化。
–R (resonance): 小磁鐵激發偵測的原理，小磁鐵和射頻脈衝間的交互作用。
–I (imaging): 訊號轉為影像的方式。
•人體及大腦中含有很多水分子，水中含有氫原子。
•磁振造影原理，是將人體或大腦置於磁場中以無線電波脈衝來改變區域磁場，激發人體組織內氫原子核的共振，而人體不同的組織，便會產生不同的磁矩變化訊號，再經過電腦處理，便可以呈現出人體組織的切面影像。
•磁振造影的磁場強度，則是以Tesla（特斯拉）磁力單位表示。
•第一部MRI 掃描儀在 1980 年代問世，到了 2002 年，全球約有 2 萬 2000 台，每年作了超過 6000 萬次的檢查。
•003 MRI 發明人 Lauterbur 和 Mansfield 獲諾貝爾醫學獎。
moodle.ncku.edu.tw/mod/resource/view.php?id=250378
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Brain Physiology, Cognition and Consciousness group: topic
This is a public discussion boardFeatured articles
Hans Peter Jobst Ricke
Wednesday, 09 September 2009 08:14 UTC
We have – since quite a while – posted articles and in order to feature them pinned them so they could catch the attention of all group members, even those who are not visiting the group on a regular basis.
Some of them did not raise many replies, so it does not make sense to have them at the top for months. Then they will possibly appear in the link collection below. In that case, just look them up and “revive” them any time you want.
This thread is going to collect those articles and also have a general discussion about interesting articles that might be worth a thread of their own. Please keep checking this place for new articles.
1. Effects on Cognition by Erythropoietin
2. Models of Consciousness
Updated 08 October 2009 10:39 UTCSome of them did not raise many replies, so it does not make sense to have them at the top for months. Then they will possibly appear in the link collection below. In that case, just look them up and “revive” them any time you want.
This thread is going to collect those articles and also have a general discussion about interesting articles that might be worth a thread of their own. Please keep checking this place for new articles.
1. Effects on Cognition by Erythropoietin
2. Models of Consciousness
Replies
This forum is closed.-
How about this one?
Classical conditioning in the vegetative and minimally conscious state
From the abstract: “Our results suggest that individuals with DOCs might have partially preserved conscious processing, which cannot be mediated by explicit reports and is not detected by behavioral assessment.” -
It is my intention to discuss with you, but it no gives me time to respond in detail(for my job). Excuse me for that and for my lack
poorof dedication.
Thanks for your comprehension.
Alejandro Correa -
Researchers crack part of the neuronal code
Together with colleagues from the Graz University of Technology, scientists from the Max Planck Institute for Brain Research in Frankfurt have succeeded in taking a step towards achieving this. They have shown that early processing stages in the brain gather information over an extended period.
How does the brain store detailed information from sensory stimuli? How much can researchers read from the activity of certain regions of the brain? Current findings confirm a new theory. Up to now, scientists had assumed that the early stages of information processing in the brain took place gradually, that is that one stimulus was processed after another in a conveyor-belt-like sequence. This idea must now be revised. As Danko Nikolic from the Max Planck Institute for Brain Research and his Austrian colleagues Wolfgang Maass and Stefan Häusler have shown, the activity in early brain areas depends on stimuli that arose some time ago. “The brain functions like a jug of water into which stones are thrown and, as a result, generate waves,” explains Nikolic. “The waves overlap but the information as to how many stones were thrown into the jug and when they were thrown in is retained in the resulting complex activity patterns of the fluid.”
The brain is clearly able to render this information usable and, for example, to superimpose images seen in succession. The duration and intensity of the continuing effect of images that have just been seen corresponds to a very detailed visual memory also known as iconic memory. If you see an image and close your eyes immediately afterwards it remains visible for a short while. It may be located in the primary visual cortex.
Original article in Phys.Org
At the risk of belaboring the obvious, the foregoing is in clear accord with my own views regarding superposition, perception and consciousness, where the waves being superposed are photonic waves/state vectors:
Are Perceptual Fields Quantum Fields?
Thus, sensory fields just are superpositions of afferent photons (in seeing, or simple sensation).
Photons contributed by memory, motor, affective and cognitive centers and so forth — these give rise to various levels of perceptual awareness, of seeing as. -
Dear Brian: Many thanks for this notice. It is becoming clear that brain cognitive states operate on “wave computing” and that this computing is different from what digital computers do. I am one of those who hold that wave computing has a quantum foundation, although I also believe that the explanation of macro systems dynamics (as the brain) should take into account complex initial and boundary conditions, as well as supplementary principles.
Best Regards
Alfredo -
Dear Alfredo,
Thanks for your reply. I’m not sure whether the material below got through on my first attempt.
I think we are in accord here with mainstream physics, as given, e.g., on pg 1 of Hawking & Ellis.
It works out very well, I think, this dual picture of waves/vectors, in respect of what we actually perceive. Thus, many people who really ought to know better persist in identifying color with wavelength — Not stopping to think that colors fill areas, whereas a wavelength is, after all, a length, and so fails a very simple dimensional test.
How do vectors help us out, though? Well, vectors are dual to differential forms (PDF), and so we have a nice way of recovering colored areas in a way that would seem perfectly compatible with the traditional tensor representation of EM — and then, the tensor representation should also give us the kinds of symmetries we observe with colors and the other secondary properties.
Shifting gears a bit, we also seem to recover a nice analogy to Hilbert space:
Again, subjecting a photon to the Doppler effect changes its energy (by E = hv) and so the energy operator rotates the photon in Hilbert space and, by a kind of Bohr-like correspondence principle, rotates the color vector as well.
In other news, here’s a fascinating item:
Golden Ratio Discovered In a Quantum World
This would seem to be a nice point of departure for a theme I’ve mentioned earlier, viz., the deep relation of sound to number — already known to Pythagoras, but still awaiting a proper explanation.
But that will have to wait for another day. -
Here is the original press release (PDF) regarding the work I cited above:
Golden ratio discovered in a quantum world
I would like to draw attention to a few major points:
When applying a magnetic field at right angles to an aligned spin the magnetic chain will transform into a new state called quantum critical, which can be thought of as a quantum version of a fractal pattern.
Fractals are characterized by self-similarity across temporal-spatial scales. I have often argued that it makes a kind of sense to suppose that “neural form follows quantum function,” in this wise:
If Paul Churchland is correct about the neural implementation of matrix-valued operators, then that is rather interesting, since that is precisely the sort of mathematics we find at work at the quantum level of neural function. Which would seem to make a kind of sense, if, as we suggest, the form of neural networks follows the underlying function of those quantum processes which mediate neural activity. Given that that the dendritic forms of neurons are aptly captured by the mathematics of fractals, we might expect this kind of self-similarity across scales.
(from: Are Perceptual Fields Quantum Fields?)
I did not know how far down the scale we could go, however — did not know how to ground fractal behavior in the quantum realm. So this is welcome news.
By a curious coincidence, a young scholar recently sent me a rather old piece by Hofstadter, where already we see fractal patterns emerging at the quantum level.
Another point of interest in the article on the golden ratio:
“Such discoveries are leading physicists to speculate that the quantum, atomic scale world may have its own underlying order. Similar surprises may await researchers in other materials in the quantum critical state.”
Well, this kind of “underlying order” suggests “hidden variables,” and in this connection I would like to draw attention to another fascinating development:
’Loopy’ Photons Test Hidden-Variable Predictions
Again, this is welcome news to me in view of the following:
Let us attend to the simplicity of colors. For colors are so simple, we might think of them as elemental, and so perhaps count them among the proper elements of an EPR-complete quantum theory. What does this mean? Let’s remind ourselves of what Einstein & Co., said in their seminal work on the (in)completeness of QM:
In attempting to judge the success of a physical theory, we may ask ourselves two questions: (1) “Is the theory correct?” and (2) “Is the description given by the theory complete?” It is only in the case in which positive answers may be given to both of these questions, that the concepts of the theory may be said to be satisfactory. The correctness of the theory is judged by the degree of agreement between the conclusions of the theory and human experience…
Whatever the meaning assigned to the term complete, the following requirement for a complete theory seems to be a necessary one: every element of the physical reality must have a counterpart in the physical theory.
We see that our investigation naturally leads us to the question: Are the secondary properties among the “hidden variables” of QM?
I would like to begin an attempt to tie all this together in respect of spectral theory and, in particular, spectral triples.
Colors and sounds come to us in the spectra of rainbows and the notes of the scale. The explanation of atomic spectra provided the first big win for QM.
Here is what Connes writes about the explanatory power of spectral triples in a very nice collection of essays edited by Majid, On Space & Time .
The new paradigm of spectral triples passes a number of tests to qualify as a replacement of Riemannian geometry in the noncommutative world:
- It contains the Riemannian paradigm as a special case.
- It does not require the commutativity of coordinates.
- It covers the spaces of leaves of foliations.
- It covers spaces of fractal, complex or infinite dimension.
- It applies to the analogue of symmetry groups (compact quantum groups).
- It provides a way of expressing the full Standard Model coupled to Einstein gravity as pure gravity on a modified spacetime geometry.
- It allows for quantum corrections to the geometry.
Thus, e.g., in one of his papers, Connes writes: “The physical action only depends on [the spectrum] Σ.”
Well, of course, the action is now known to be determined by the symmtries of nature (Weinberg, e.g.), and so we have a direct route to the Lagrangian and very nearly all of classical & quantum mechanics:
Roughly speaking, force is the space derivative of energy and the time derivative of momentum. You can take one more step up the ladder: energy and momentum are both derivatives of action: energy is its time derivative, momentum its space derivative. (Wilczek)
Finally, we see instances of field behavior influenced by number — in the transcendental golden ratio and in Hofstadter’s rational and irrational numbers. I earlier alluded to the well-known relations between musical tones and numerical ratios — and here again it seems as though Nature is hinting at wonderful things remaining to be discovered.
Now, the foregoing is obviously all very rough and preliminary, but it seems like a promising avenue for further exploration. -
I’d like to add a few more notes and links apropos “a natural geometry for bringing these various developments under one roof.”
Connes writes that: The new paradigm of spectral triples passes a number of tests to qualify as a replacement of Riemannian geometry in the noncommutative world.
In a very nice older paper, Kline wrote that “the elliptic non-Euclidean geometry created by Riemann can also be derived as special cases of projective geometry.”
[It] became possible to affirm that projective geometry is indeed logically prior to Euclidean geometry and that the latter can be built up as a special case. Both Klein and Arthur Cayley showed that the basic non-Euclidean geometries developed by Lobachevsky and Bolyai and the elliptic non-Euclidean geometry created by Riemann can also be derived as special cases of projective geometry. No wonder that Cayley exclaimed, “Projective geometry is all geometry.”
My interest in these issues came by way of Weyl:
Mathematics has introduced the name isomorphic representation for the relation which according to Helmholtz exists between objects and their signs. I should like to carry out the precise explanation of this notion between the points of the projective plane and the color qualities […] the projective plane and the color continuum are isomorphic with one another. Every theorem which is correct in the one system Σ1 is transferred unchanged to the other Σ2. A science can never determine its subject matter except up to an isomorphic representation. The idea of isomorphism indicates the self-understood, insurmountable barrier of knowledge. It follows that toward the “nature” of its objects science maintains complete indifference. This for example what distinguishes the colors from the points of the projective plane one can only know in immediate alive intuition […]
Kline continues, introducing the vital topic of mathematical duality:
The principle of duality in projective geometry states that we can interchange point and line in a theorem about figures lying in one plane and obtain a meaningful statement. Moreover, the new or dual statement will itself be a theorem—that is, it can be proven. On the basis of what has been presented here we cannot see why this must always be the case for the dual statement. However, it is possible to show by one proof that every rephrasing of a theorem of projective geometry in accordance with the principle of duality must be a theorem. This principle is a remarkable characteristic of projective geometry. It reveals the symmetry in the roles that point and line play in the structure of that geometry.
So it seems as though we are on secure ground, passing from the picture of colors-as-vectors to the picture of colors-as-forms, because vectors and forms are dual to one another.
I’ve recently found two more nice pieces on projective geometry, one from Dirac (PDF) and a philosophical commentary on his paper; I pass them along here for their historical interest:
Projective Geometry, Origin of Quantum Equations
Dirac’s hidden geometry
Finally, I was wondering how one might reconcile spectral triples with projective geometry and found the following (PDF) article, which looks promising:
Applications of Spectral Geometry to A ne and Projective Geometry
And a collection of confrence papers:
Algebras, Operators and Noncommutative Geometry -
One of the many ill-informed, knee-jerk reactions to the ‘quantum-mind’ program told us that the brain is too warm, wet and noisy for quantum effects to be important.
I have often replied that we live in a quantum universe and that all physical effects are ipso facto quantum effects. Thus, e.g., Freeman Dyson: “There is nothing else except these [quantum] fields: the whole of the material universe is built of them.”* This would seem to severely limit our choices as to the neural correlates of consciousness (NCC) — and wonderfully so, radically constraining the solution set.
I have also pointed out that the oceans are warm, wet and noisy — and yet its inhabitants regularly send and receive “coherent” signals, as when whales break into song. Well, but oceans are surely classical objects and so with whales and their vocalizations. Here is Dyson to help us out again:
“Physicists talk about two kinds of fields: classical fields and quantum fields. Actually, we believe that all fields in nature are quantum fields. A classical field is just a special large-scale manifestation of a quantum field.” (My emphasis)
No argument, however clear, can summon the force of a living example, however, and so I am pleased to report more evidence from our friends, the vegetables.
Nature’s hot green quantum computers revealed
NewScientist 03 February 2010 by Kate McAlpine
WHILE physicists struggle to get quantum computers to function at cryogenic temperatures, other researchers are saying that humble algae and bacteria may have been performing quantum calculations at life-friendly temperatures for billions of years.
The evidence comes from a study of how energy travels across the light-harvesting molecules involved in photosynthesis. The work has culminated this week in the extraordinary announcement that these molecules in a marine alga may exploit quantum processes at room temperature to transfer energy without loss. Physicists had previously ruled out quantum processes, arguing that they could not persist for long enough at such temperatures to achieve anything useful.
Photosynthesis starts when large light-harvesting structures called antennas capture photons. In the alga called Chroomonas CCMP270, these antennas have eight pigment molecules woven into a larger protein structure, with different pigments absorbing light from different parts of the spectrum. The energy of the photons then travels across the antenna to a part of the cell where it is used to make chemical fuel.
The route the energy takes as it jumps across these large molecules is important because longer journeys could lead to losses. In classical physics, the energy can only work its way across the molecules randomly. “Normal energy transfer theory tells us that energy hops from molecule to molecule in a random walk, like the path taken home from the bar by a drunken sailor,” says Gregory Scholes at the University of Toronto, Canada, one of the co-authors of the paper published in Nature this week.
- “Field Theory” Scientific American, 188, No. 4, April 1953, pp. 57-64.
-
This might be of interest; a video of a seminar held at the University of Bristol, the presentation is easy going and informative.
Materials for Photonic Quantum Information, by JG Rarity -
Electrophysiological models of neural processing
by Mark E. Nelson
The brain is an amazing information processing system that allows organisms
to adaptively monitor and control complex dynamic interactions with their
environment across multiple spatial and temporal scales. Mathematical modeling
and computer simulation techniques have become essential tools in understanding diverse aspects of neural processing ranging from sub-millisecond temporal coding in the sound localization circuity of barn owls to long-term memory storage and retrieval in humans that can span decades. The processing capabilities of individual neurons lie at the core of these models, with the emphasis shifting upward and downward across different levels of biological organization depending on the nature of the questions being addressed. This review provides an introduction to the techniques for constructing biophysically based models of individual neurons and local networks. Topics include Hodgkin-Huxley-type models of macroscopic membrane currents, Markov models of individual ion channel currents, compartmental models of neuronal morphology, and network models involving synaptic interactions among multiple neurons.
Wiley InterScience Focus Article
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