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Tero Toivanen

AK's Rambling Thoughts: Nerve Cells and Glial Cells: Redefining the Foundation of Intel... - 0 views

artksthoughts.blogspot.com/...nd-glial-cells-redefining.html

brain Glial Cells neuron action potential axon synapse network microglia macroglia astrocytes oligodendrocytes ependymal cells radial glia

shared by Tero Toivanen on 25 Jun 09 - Cached
  • Glia are generally divided into two broad classes, microglia and macroglia. Microglia are part of the immune system, specialized macrophages, and probably don't participate in information handling. Macroglia are present in both the peripheral and central nervous systems, in different types.
  • Traditionally, there were four types of glia in the CNS: astrocytes, oligodendrocytes, ependymal cells, and radial glia. Of these, the one type that's most important to the developing revolution in our ideas are those cells called astrocytes.2 It turns out that there are at least two types of cell (at least) subsumed under this name.24, 25, 31, 32 One, which retains the name of astrocyte, takes up neurotransmitters released by neurons (and glial cells), aids in osmoregulation,10 controls circulation in the brain,1, 31 and generally appears to provide support for the neurons and other types of glia.
  • Although both NG2-glia and astrocytes extend processes to nodes of Ranvier in white matter ([refs]) and synapses in grey matter, their geometric relationship to these neuronal elements is different. Thus, although astrocytes and NG2-glia bear a superficial resemblance, they are distinguished by their different process arborizations. This will reflect fundamental differences in the way these two glial cell populations interact with other elements in the neural network.
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  • Both types of glia are closely integrated with the nervous system, receiving information from action potentials via synapses22 (which, only a few years ago were thought to be limited to neurons), and returning control of neuron activity through release of neurotransmitters and other modulators. Both, then, demonstrate the potential for considerable intelligent activity, contributing to the overall intelligence of the brain.
  • Astrocytes probably (IMO) are limited, or mostly so, to maintaining the supplies of energy and necessary metabolites. They receive action potentials,3, 6 which allows them to closely and quickly monitor general activity and increase circulation in response, even before the neurons and NG2-glia have reduced their supply of ATP.21 They appear to be linked in a network among themselves,2, 5 allowing them to communicate their needs without interfering with the higher-level calculations of the brain.
  • NG2-glia appear to have several functions, but one of the most exciting things about them is that they seem to be able to fire action potentials.33 Their cell membranes, like those of the dendrites of neurons, have all the necessary channels and receptors to perform real-time electrical calculations in the same way as neural dendrites. They have also demonstrated the ability to learn through long term potentiation.
  • Dividing NG2-glia also retain the ability to fire action potentials, as well as receiving synaptic inputs from neurons.23 Presumably, they continue to perform their full function, including retaining any elements of long term potentiation or depression contained in their synapses.
  • Oligodendrocytes are responsible for the insulation of the axons, wrapping around approximately 1 mm of each of up to 50 axons within their reach, and forming the myelin sheath.
  • Although the precise type of neuron formed by maturing cells hasn't been determined, the very fact that cells of this type can change into neurons is very important. We actually don't know whether the cells that do this maturation are the same as those that perform neuron-like activities, there appear to be two separate types of NG2-glia, spiking and non-spiking.26 It may very well be that the "spiking" type have actually differentiated, while the "non-spiking" type may be doing the maturing. Of course, very few differentiated cell types remain capable of division, as even the "spiking" type do.
  • What's important about both dendrites and NG2-glia isn't so much their ability to propagate action potentials, as that their entire cell membranes are capable of "intelligent" manipulation of the voltage across it.
  • While there are many ion channels involved in controlling the voltage across the cell membrane, the only type we really need to worry about for action potentials is voltage-gated sodium channels. These are channels that sometimes allow sodium ions to pass through the cell membrane, which they will do because the concentration of sodium ions outside the cell is very much higher than inside. When and how much they open depends, among other things, on the voltage across the membrane.
  • A normal neuron will have a voltage of around -60 to -80mV (millivolts), in a direction that tends to push the sodium ions (which are positive) into the cell (the same direction as the concentration is pushing). When the voltage falls to around -55mV, the primary type of gate will open for a millisecond or so, after which it will close and rest for several milliseconds. It won't be able to open again until the voltage is somewhere between -55 and around -10mV. Meanwhile, the sodium current has caused the voltage to swing past zero to around +20mV.
  • When one part of the cell membrane is "depolarized" in this fashion, the voltage near it is also depressed. Thus, if the voltage is at zero at one point, it might be at -20mV 10 microns (μm) away, and -40mV 20μm away, and -60mV 30μm, and so on. Notice that somewhere between 20μm and 30μm, it has passed the threshold for the ion channels, which means that they are open, allowing a current that drives the voltage further down. This will produce a wave of voltage drop along the membrane, which is what the action potential is.
  • After the action potential has passed, and the gates have closed (see above), the voltage is recovered by diffusion of ions towards and away from the membrane, the opening of other gates (primarily potassium), and a set of pumps that push the ions back to their resting state. These pumps are mostly powered by the sodium gradient, except for the sodium/potassium pump that maintains it, which is powered by ATP.
  • the vast majority of calculation that goes into human intelligence takes place at the level of the network of dendrites and NG2-glia, with the whole system of axons, dendrites, and action potentials only carrying a tiny subset of the total information over long distances. This is especially important considering that the human brain has a much higher proportion of glial matter than our relatives.
  • This, in turn, suggests that our overall approach to understanding the brain has been far too axon centric, there needs to be a shift to a more membrane-centric approach to understanding how the brain creates intelligence.
  • Tero Toivanen on 25 Jun 09
     
    Our traditional idea of how the brain works is based on the neuron: it fires action potentials, which travel along the axon and, when the reach the synapses, the receiving neuron performs a calculation that results in the decision when (or whether) to fire its own action potential. Thus, the brain, from a thinking point of view, is viewed as a network of neurons each performing its own calculation. This view, which I'm going to call the axon-centric view, is simplistic in many ways, and two recent papers add to it, pointing up the ways in which the glial cells of the brain participate in ongoing calculation as well as performing their more traditional support functions.
Tero Toivanen

Neurophilosophy : Experience induces global reorganization of brain circuitry - 0 views

scienceblogs.com/...ization_of_brain_circuitry.php

neurophilosophy brain LTP learning memory

shared by Tero Toivanen on 23 May 09 - Cached
  • Now referred to as long-term potentiation (LTP), this mechanism has since become the most intensively studied in modern neuroscience,and is widely believed to be the cellular basis of learning and memory, although this is yet to be proven unequivocally.
  • In the new study, Santiago Canals of the Max Planck Institute for Biological Cybernetics in Tübingen and his colleagues used the same protocol to induce LTP. But while the vast majority of researchers have investigated LTP in slices of hippocampal tissue, this study involved observing LTP in live animals.
  • This new research provides the first evidence that the local modifications in synaptic connections induced by LTP lead to long-lasting changes in the activity of a diffuse network of brain regions, and even to facilitated communication between the two hemispheres. The fMRI data showed that hippocampal LTP recruits higher order association areas, as well as regions involved in emotions and others subserving different sensory modalities, all of which are known to be involved in memory formation.
  • Tero Toivanen on 23 May 09
     
    Experience induces global reorganization of brain circuitry. This new research provides the first evidence that the local modifications in synaptic connections induced by LTP lead to long-lasting changes in the activity of a diffuse network of brain regions, and even to facilitated communication between the two hemispheres.
Tero Toivanen

Guitars And Brains: Neuroscience Synchronization Happens In Musical Duets - 0 views

www.science20.com/...on_happens_musical_duets-97503

brain guitars brains neuroscience synchronization music

shared by Tero Toivanen on 02 Dec 12 - No Cached
  • Tero Toivanen on 02 Dec 12
     
    "The current data indicate that synchronization between individuals occurs in brain regions associated with social cognition and music production. And such interbrain networks are expected to occur not only while performing music. "We think that different people's brain waves also synchronise when people mutually coordinate their actions in other ways, such as during sport, or when they communicate with one another," Sänger says."
Tero Toivanen

How the Brain Forms Categories | Neuroscience News - 0 views

neurosciencenews.com/rms-categories-neural-networks

brain research neuroscience neurons learning category categories

shared by Tero Toivanen on 21 Oct 12 - No Cached
  • Tero Toivanen on 21 Oct 12
     
    "...amazing skill of our brain to turn a wealth of sensory information into a number of defined categories and objects"
David McGavock

Scientific Understanding of Consciousness - 0 views

willcov.com/bio-consciousness

understanding consciousness experts writers summary

shared by David McGavock on 02 Mar 14 - No Cached
  • During the past 20 years or so, biological sciences have advanced to the point that scientists have begun researching biological mechanisms of brain function and suggesting some reasonably well-founded hypotheses for consciousness. Leading the way in these pioneering efforts, in my judgment, have been:   Gerald Edelman with his hypothesis of the Dynamic Core, Antonio Damasio with his concepts of  Protoself, Core Self, Autobiographical Self, Core Consciousness and Extended Consciousness, Joseph LeDoux and his emphasis on the intricacies of synapses and the emotional brain,
  • Rudolfo Llinás and his researches into ~40 Hz oscillations and synchronization, György Buzsáki with his discussion and exploration of neural mechanisms related to oscillation and synchronization in the neocortex and hippocampus for perception and memory, Joaquín Fuster, the world’s preeminent expert on the frontal lobes, and his concept of the "perception-action cycle," Susan Greenfield's notion of "neuronal gestalts" as a way of conceptualizing a highly variable aggregation of neurons that is temporarily recruited around a triggering epicenter. I use the neuronal gestalts idea in my way of visualizing the functionality of the dynamic core of the thalamocortical system, Eric Kandel who has explored short-term and long-term memory,
  • The late Francis Crick with his collaborator Christof Koch who have pursued the neural correlate of consciousness (NCC), Michael Gazzaniga with the concept of the left hemisphere ‘interpreter’ unifying consciousness experience, Edmund Rolls and Gustavo Deco with their mathematical models of brain function using information theory approaches for biologically plausible neurodynamical modeling of cognitive phenomena corroborated by brain imaging studies, David LaBerge with his discussion of the thalamocortical circuit and attention, Alan Baddeley who continues to refine his model for working memory, Philosopher John Searle who endorses the idea that consciousness is an emergent property of neural networks.
  • David McGavock on 02 Mar 14
     
    "My objective in this website has been to bring together salient features of these assorted interpretations by science experts into a synthesis of my own understanding of consciousness. I consider these statements and interpretations to be a framework on which to build a fuller understanding as further data, concepts and insights develop from ongoing research."
Tero Toivanen

Scientists capture the first image of memories being made - 0 views

www.eurekalert.org/...mu-sct061809.php

brain memory protein translation long-term memory proteins synapse synaptic connection learning synaptic plasticity post-synaptic cell neurons

shared by Tero Toivanen on 21 Jun 09 - Cached
  • A new study by researchers at the Montreal Neurological Institute and Hospital (The Neuro), McGill University and University of California, Los Angeles has captured an image for the first time of a mechanism, specifically protein translation, which underlies long-term memory formation. The finding provides the first visual evidence that when a new memory is formed new proteins are made locally at the synapse - the connection between nerve cells - increasing the strength of the synaptic connection and reinforcing the memory. The study published in Science, is important for understanding how memory traces are created and the ability to monitor it in real time will allow a detailed understanding of how memories are formed.
  • research has focused on synapses which are the main site of exchange and storage in the brain.
  • They form a vast but also constantly fluctuating network of connections whose ability to change and adapt, called synaptic plasticity, may be the fundamental basis of learning and memory.
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  • Using a translational reporter, a fluorescent protein that can be easily detected and tracked, we directly visualized the increased local translation, or protein synthesis, during memory formation.
  • Importantly, this translation was synapse-specific and it required activation of the post-synaptic cell, showing that this step required cooperation between the pre and post-synaptic compartments, the parts of the two neurons that meet at the synapse.
  • This study provides evidence that a mechanism that mediates this gene expression during neuronal plasticity involves regulated translation of localized mRNA at stimulated synapses.
  • Tero Toivanen on 21 Jun 09
     
    A new study by researchers at the Montreal Neurological Institute and Hospital (The Neuro), McGill University and University of California, Los Angeles has captured an image for the first time of a mechanism, specifically protein translation, which underlies long-term memory formation.
Tero Toivanen

Adult Learning - Neuroscience - How to Train the Aging Brain - NYTimes.com - 1 views

www.nytimes.com/...03adult-t.html

neuroscience brain aging adult learning tots research training

shared by Tero Toivanen on 02 Jan 10 - Cached
  • One explanation for how this occurs comes from Deborah M. Burke, a professor of psychology at Pomona College in California. Dr. Burke has done research on “tots,” those tip-of-the-tongue times when you know something but can’t quite call it to mind. Dr. Burke’s research shows that such incidents increase in part because neural connections, which receive, process and transmit information, can weaken with disuse or age.
  • But she also finds that if you are primed with sounds that are close to those you’re trying to remember — say someone talks about cherry pits as you try to recall Brad Pitt’s name — suddenly the lost name will pop into mind. The similarity in sounds can jump-start a limp brain connection. (It also sometimes works to silently run through the alphabet until landing on the first letter of the wayward word.)
  • Recently, researchers have found even more positive news. The brain, as it traverses middle age, gets better at recognizing the central idea, the big picture. If kept in good shape, the brain can continue to build pathways that help its owner recognize patterns and, as a consequence, see significance and even solutions much faster than a young person can.
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  • The trick is finding ways to keep brain connections in good condition and to grow more of them.
  • Educators say that, for adults, one way to nudge neurons in the right direction is to challenge the very assumptions they have worked so hard to accumulate while young. With a brain already full of well-connected pathways, adult learners should “jiggle their synapses a bit” by confronting thoughts that are contrary to their own, says Dr. Taylor, who is 66.
  • Teaching new facts should not be the focus of adult education, she says. Instead, continued brain development and a richer form of learning may require that you “bump up against people and ideas” that are different. In a history class, that might mean reading multiple viewpoints, and then prying open brain networks by reflecting on how what was learned has changed your view of the world.
  • Such stretching is exactly what scientists say best keeps a brain in tune: get out of the comfort zone to push and nourish your brain. Do anything from learning a foreign language to taking a different route to work.
  • “As adults we have these well-trodden paths in our synapses,” Dr. Taylor says. “We have to crack the cognitive egg and scramble it up. And if you learn something this way, when you think of it again you’ll have an overlay of complexity you didn’t have before — and help your brain keep developing as well.”
  • Tero Toivanen on 02 Jan 10
     
    Dr. Burke has done research on "tots," those tip-of-the-tongue times when you know something but can't quite call it to mind. Dr. Burke's research shows that such incidents increase in part because neural connections, which receive, process and transmit information, can weaken with disuse or age.
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