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Are regions of cortex actually defined by astrocytic syncytia?
Almost certainly
0%
 0%  [ 0 ]
It appears likely
0%
 0%  [ 0 ]
Perhaps, deserves immediate attention
33%
 33%  [ 1 ]
Unlikely
66%
 66%  [ 2 ]
Total Votes : 3


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Cephavi


Joined: 06 Jul 2005
Posts: 6

07-06-05, 04:18 pm
PostPost subject: The Astrocyte Hypothesis Reply with quote

Hierarchies of action potential-driven neurons may prove insufficient to accurately model human cognition. Astrocytes, ten times more plentiful than neurons in the human brain, may prove to be a key missing element of the memory-prediction framework.

I recently stumbled across a well written monograph entitled, A Theory of Cortical Neuron-Astrocyte Interaction, written by Dale Stanley Antanitus, M.D., Department of Pediatrics, Harvard Medical School. I encourage everyone to read it, http://www.antanitus.com/hypothesis/. Here's an excerpt:

"It has traditionally been held that associative cortical integration of sensory input is accomplished purely through utilization of complex networks of neuronal connections. The theory presented here, however, contends that the associative areas of brain include plastic, motile astrocytes that participate in the encoding and manipulation of information by organizing and controlling groups of synapses. Sensory information that began its journey as neuronal action potentials eventually reaches areas of the central nervous system in patterns that activate astrocytic calcium waves. According to the theory, activated astrocytes in turn infotropically encode the information with resulting synchronously firing synaptic domains. The character of the synaptic domains reflects the primary perceived sensory information at any moment in time, but the pools of synchronous synapses are modified by the presentation of novel information. Through the mechanism of infotropic astrocytic movement, metaphorically speaking, `the input changes the hardware.'"

After reading the theory, please consider responding to the following poll question.
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Orion


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Location: Reed City, Michigan, U.S.

07-14-05, 07:19 am
PostPost subject: heythere! Reply with quote

IT seems to me, according to your blurb, that these cells merely support the activty of neurons--- meaning everything can still be explained by neural behavior, though neural behavior must be explained by astrocyte behavior. Neural columns are still the cheif structure, regardless of who is doing the work. Study of neural column behavior can be carried out seperately of any constituent cells whatsoever (to an extent); thus, columns could be made of glial cells, neurons, astrocytes, or whatever. It matters little; the same end behavior is acheived, and the end behavior is important, not how to get there. There are probably many possible ways to get there--- including circutry, which has no astrocytes whatsoever.

Of course, it is important to determine the exact role of astrocites ands other cells. But the "emergent behavior" can be studied seperately of the components.
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Cephavi


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07-14-05, 11:10 am
PostPost subject: Reflecting the I Reply with quote

One of the major goals of the MPF, if not the major goal, is to model the neocortex accurately enough to produce artificial intelligence. It seems to me that such efforts are almost certainly compromised by the absence of key foundational elements.

Your point is like saying 'atoms are atoms, their constituent elements are irrelevant.' To imply that 'the how' is unimportant seems almost absurd in the present context; this is, presumably, a scientific discussion. Your statement that 'circuitry has no astrocytes whatsoever' is equally disappointing. You seem to have missed the whole point.

With the MPF and Numenta, Jeff Hawkins is not merely 'studying' the underlying mechanism of intelligence, he's attempting to construct a working model of it. For that model to work, all major system elements must be understood and simulated. My point with this thread is to spotlight a major system element that has thus far gone ignored. Astrocytic syncytia may be the key to understanding cortical regionalization, that is, how regions of cortex form and change over time. This behavior, so obviously instrumental to memory and learning, must be modeled and simulated if the AI is to properly reflect the I.
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Cephavi


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07-14-05, 12:33 pm
PostPost subject: Gamma Synchrony Reply with quote

From the Brain Dynamic Centre, University of Sydney:

"Recently there has been a growing awareness amongst scientists that the reductionistic approach to characterizing brain function which has underpinned much previous research, whilst providing profoundly important insights regarding brain activity, nonetheless yields only an incomplete picture of how the brain operates as a system. The reductionistic approach involves examining brain processing activities by breaking them down into smaller and smaller sub-components, each of which is examined largely in isolation from other processes. Such an approach provides an incomplete account of brain function because it does not address the issue of how these spatially diffuse processing sub-components are integrated with each other. More specifically, given that the brain engages parallel distributed processes and does not function in a serial manner, different processes in the brain at any one time will be related to a greater or lesser extent to other processes occurring in different regions at the same time. The question arises how the brain keeps track of and operates on these relationships between different processes. This is known as the binding problem.

"Of central importance in this regard is a kind of high-frequency neuronal oscillation observed in the brain called gamma activity. It is thought that synchronization of gamma oscillations between different regions of the brain involved in related processing may be a mediator of binding. Evidence that spatially distributed synchronous gamma oscillations might play a role in binding originally emerged from animal experiments, particularly in visual processing during the early 1990s. Since then a considerable body of direct and indirect evidence has emerged linking these oscillations with cognitive binding in a wide range of contexts, primarily from animal experiments, but also from studies in humans. In addition, simulation studies and models of neuronal dynamics have increasingly pointed to synchrony as an important possible coding mechanism."

From Stuart Hameroff, Director, Center for Consciousness Studies, University of Arizona:

"In recent years gamma synchrony has indeed been shown to derive not from axonal spikes and axonal-dendritic synapses, but from post-synaptic activities of dendrites. Specifically, gamma synchrony/40 Hz is driven by networks of cortical inter-neurons connected by dendro-dendritic “electrotonic” gap junctions, windows between adjacent cells. Groups of neurons connected by gap junctions share a common membrane and fire synchronously, behaving (as Eric Kandel says) “like one giant neuron.” Gap junctions have long been recognized as prevalent and important in embryological brain development, but gradually diminish in number (and presumably importance) as the brain matures. Five years ago gap junctions were seen as irrelevant to cognition and consciousness. However more recently, relatively sparse gap junction networks in adult brains have been appreciated and shown to mediate gamma synchrony/40 Hz. Such networks are transient, coming and going like the wind (and Hebbian assemblies), as gap junctions form, open, close and reform elsewhere (regulated by intraneuronal activities). Therefore neurons (and glia) fused together by gap junctions form continually varying syncytia, or Hebbian “hyper-neurons” whose common membranes depolarize coherently and may span wide regions of cortex. (The internal cytoplasm of hyper-neurons is also continuous, prompting suggestions they may host brain-wide quantum states.) By virtue of their relation to gamma synchrony, gap junction hyper-neurons may be the long-sought neural correlate of consciousness (NCC)."

Gamma synchrony/40 Hz, the human brainbeat, is most likely anchored in the machinery of the astrocytic syncytia (hyper-neurons) and their reciprocal, neurotransmitter-induced calcium waves. These same syncytia may also provide the underlying structure for the neuronal hierarchies upon which the MPF depends.
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Orion


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07-22-05, 12:51 pm
PostPost subject: Yea, alright Reply with quote

You are right, I overstated my point. (I do that rather often...) But what connection could all this have to the memory-prediction framework? Particularly, I have been wondering how "vibrations" (if I may use the term) in the neurons could possibly go with the memory-prediction framework.
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Cephavi


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07-22-05, 01:45 pm
PostPost subject: It's the Regions Reply with quote

We've all made the mistake of overstatement. Good for you to admit it.

The connection is in Hawkins' regions of cortex, the fundamental units of the MPF. How are they held together? How do they form and change? Hawkins doesn't explain the neurophysiology of Hebbian learning beyond saying that neurons that fire together wire together (On Intelligence, p. 164). Antanitus does explain the neurophysiology, and very well I think. In short, I believe it's only a matter of time before the right people embrace the synergy between these two theories.

As for your vibrations, what basis do they have in scientific reality? If they have such a basis, why aren't you referring to them by their proper name? If they have no basis that you know of, but you feel strongly about them, you need to do your homework. Are you talking about action potentials? If so, study the nice summary at Wikipedia. It's a great place to learn and explore.
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07-23-05, 09:01 am
PostPost subject: Reply with quote

The papers you quote say "oscillations" instead of "vibrations", and a book I have speaks of "interference patterns" in the brain, which can only occur if there are waveforms. Gamma waves and other forms of brainwaves would seem to propogate information independantly of columns; according to the book, columns do not fluctuate on and off when they are active, but remain on. (Perhaps I am incorrect about this.) So it seems as if wave-activity is seperate from the primary activity of the neural columns.
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Cephavi


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07-23-05, 09:47 am
PostPost subject: Firing rate Reply with quote

Consciousness appears to be strongly linked to gamma synchrony, which theoretically involves assemblies (syncytia) of synchronously firing regions of cortex formed by gap junctions, both neuronal and astrocytic. The frequency of gamma synchrony is determined by the neuronal firing rate in those syncytia. The fact that particular columns remain on means they're constantly firing, not that there's one long columnar action potential that continues until deactivation. Wave activity is not separate from the firing of cortical columns, its frequency is the rate of that firing.
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07-24-05, 12:07 pm
PostPost subject: Reply with quote

Alright, that makes sense. Does the frequency indicate anything in particular? The book I referred to (from 1981) suggests that different waveforms stand for different images coming from the eye.
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