Brain avalanches => Neurosignatures!

[bernard]

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=14657176

http://www.jneurosci.org/cgi/content/full/23/35/11167

Neurosci. 2003 Dec 3;23(35):11167-77.
Neuronal avalanches in neocortical circuits.

Beggs JM, Plenz D. plenzd@intra.nimh.nih.gov

Unit of Neural Network Physiology, Laboratory of Systems Neuroscience, National Institute of Mental Health, Bethesda, Maryland 20892-4075, USA.

Networks of living neurons exhibit diverse patterns of activity, including oscillations, synchrony, and waves. Recent work in physics has shown yet another mode of activity in systems composed of many nonlinear units interacting locally. For example, avalanches, earthquakes, and forest fires all propagate in systems organized into a critical state in which event sizes show no characteristic scale and are described by power laws. We hypothesized that a similar mode of activity with complex emergent properties could exist in networks of cortical neurons. We investigated this issue in mature organotypic cultures and acute slices of rat cortex by recording spontaneous local field potentials continuously using a 60 channel multielectrode array. Here, we show that propagation of spontaneous activity in cortical networks is described by equations that govern avalanches. As predicted by theory for a critical branching process, the propagation obeys a power law with an exponent of -3/2 for event sizes, with a branching parameter close to the critical value of 1. Simulations show that a branching parameter at this value optimizes information transmission in feedforward networks, while preventing runaway network excitation. Our findings suggest that "neuronal avalanches" may be a generic property of cortical networks, and represent a mode of activity that differs profoundly from oscillatory, synchronized, or wave-like network states. In the critical state, the network may satisfy the competing demands of information transmission and network stability.

PMID: 14657176 [PubMed - indexed for MEDLINE]v

[nari]

This is a very encouraging paper, Bernard, and as I read the abstract, it seemed that Barrett must have had something to do with it!

Critical states, avalanches, forest fires - (I thought I had invented the forest fire bit - bother!!! Somebody stole my thunder).

It reminds me of several people I have seen this week, all in critical states of pain, all in severe emotional turmoil through nasty social histories, and one who in the grip of suicidal ideation - but that is another story...... (it has not been a good week).

I think I shall start a new thread in a more positive light...in the PP Management forum.

Nari

[bernard]

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15175392

J Neurosci. 2004 Jun 2;24(22):5216-29.
Neuronal avalanches are diverse and precise activity patterns that are stable for many hours in cortical slice cultures.

Beggs JM, Plenz D.

Unit of Neural Network Physiology, Laboratory of Systems Neuroscience, National Institute of Mental Health, Bethesda, Maryland 20892, USA.

A major goal of neuroscience is to elucidate mechanisms of cortical information processing and storage. Previous work from our laboratory (Beggs and Plenz, 2003) revealed that propagation of local field potentials (LFPs) in cortical circuits could be described by the same equations that govern avalanches. Whereas modeling studies suggested that these "neuronal avalanches" were optimal for information transmission, it was not clear what role they could play in information storage. Work from numerous other laboratories has shown that cortical structures can generate reproducible spatiotemporal patterns of activity that could be used as a substrate for memory. Here, we show that although neuronal avalanches lasted only a few milliseconds, their spatiotemporal patterns were also stable and significantly repeatable even many hours later. To investigate these issues, we cultured coronal slices of rat cortex for 4 weeks on 60-channel microelectrode arrays and recorded spontaneous extracellular LFPs continuously for 10 hr. Using correlation-based clustering and a global contrast function, we found that each cortical culture spontaneously produced 4736 +/- 2769 (mean +/- SD) neuronal avalanches per hour that clustered into 30 +/- 14 statistically significant families of spatiotemporal patterns. In 10 hr of recording, over 98% of the mutual information shared by these avalanche patterns were retained. Additionally, jittering analysis revealed that the correlations between avalanches were temporally precise to within +/-4 msec. The long-term stability, diversity, and temporal precision of these avalanches indicate that they fulfill many of the requirements expected of a substrate for memory and suggest that they play a central role in both information transmission and storage within cortical networks.

PMID: 15175392 [PubMed - indexed for MEDLINE]

[bernard]

Nari,

I think that is a critical state, for sure, but the analogies with fires and avalanches seems to me inappropriate in that case.

I will replace the term avalanches/fires by funnel.

The process is simple!

And efficicy is marvelous. One more time, Nature shows us a lesson of Simplicity and solves complex problems, just in time!

I'll wait a bit to see if there is some readers interested in the subject?

[bernard]

Here is two pdf versions

Forest Fires (http://www.somasimple.com/pdf_files/forest_fires.pdf)

And the one cited previously:
Neuronal Avalanches (http://www.somasimple.com/pdf_files/neuronal_avalanches.pdf)

[Diane]

Honestly Bernard, you are much faster than I am. (I hadn't got around to posting it here yet.. )

Wow. You've taken this topic (which has sat idle for days on the other two forums) and have dug up other papers about it and dissected it and analysed it and compared it to neurosignatures all in one sleep of mine. You are like a fairy godfather. I wouldn't have gotten back to it for weeks or months probably... and I'll probably transfer your good detective work over to PTtalk unless you have already done it... You could start a thread there...

I love the Neuronal Avalanche paper in its entirety, thanks so much Bernard.
We are being a group mind in cyberland. I look forward to your ideas on 'cooperation' being a key feature in memory aquisition. It will echo Lynn Margulis who asserts that cooperation was the key to successful continued existance in the early earth days among the protocists. Without their cooperative ventures in hard times, multicell life would not have come into existance, period.

Nari, I'm pretty sure I never read about forest fires as metaphor for nervous systems until you brought it up.
Diane

[bernard]

Hi SomaSimplers,

1/ what contains a memory event or a neurotag/neurosignature?
I may say a lot of things and because it contains a lot, it is complex!

An memory event is often a collection of many senses' events. A pain state is also a sort of memory event. It may contains a location (where did it happened?), an olfactory data, a sound, a taste of touch, a movement realized with these muscles...

We may say with many evidences that many parts/centres of brain are involved and are working to make a snapshot of the world around us. All these centres work for their own at the beginning but may share or not their findings to produce a more complex collection.

Our eyes may see a flower and our brain worked in many areas to recognise a flower, a perfume, a shape, a colour, some memories, a pin... But seeing a flower may not produce a memory if nothing push ourselves to remember it...

So, we have many processes running not necessarily in synchrony since some events are treated in their owns areas with their speeds. There are too much neurons involved to produce a simple memory event?

[bernard]

Hi SomaSimplers,

We have now components of a possible memory (event) but they need to be triggered before being registered. When we recall a souvenir, we recall many components and the only way to do it, is to activate the trigger once again. The trigger is in fact a neural network which light up all the components in sequence where they appeared (or were perceived).

This trigger is of course a neurosignature.

Some constraints may arise if we tried to memorize all the original components which were composing the memory event. It will consume/cost too much resources (neurones/connections). It is preferable to collect all the bits of partial memory (light, colour, sound...) and activate them to re-create a trigger with them.

But it does not give the solution of this avalanche of neuronal activations. In fact, we have a very large collection of enabled neurons and we want a simple network which is containing the indispensable elements. It is like a funnel => it permits to collect large collection and reduces it in a defined shape...

[bernard]

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15673441

Eur J Neurosci. 2005 Jan;21(2):422-30. Related Articles, Links
Click here to read
Activity-dependent maturation of excitatory synaptic connections in solitary neuron cultures of mouse neocortex.

Takada N, Yanagawa Y, Komatsu Y.

Department of Visual Neuroscience, Research Institute of Environmental Medicine, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan.

Activity plays important roles in the formation and maturation of synaptic connections. We examined these roles using solitary neocortical excitatory neurons, receiving only self-generated synaptic inputs, cultured in a microisland with and without spontaneous spike activity. The amplitude of excitatory postsynaptic currents (EPSCs), evoked by applying brief depolarizing voltage pulses to the cell soma, continued to increase from 7 to 14 days in culture. Short-term depression of EPSCs in response to paired-pulse or 10-train-pulse stimulation decreased with time in culture. These developmental changes were prevented when neurons were cultured in a solution containing tetrodotoxin (TTX). The number of functional synapses estimated by recycled synaptic vesicles with FM4-64 was significantly smaller in TTX-treated than control neurons. However, the miniature EPSC amplitude remained unchanged during development, irrespective of activity. Transmitter release probability, assessed by use-dependent blockade of N-methyl-d-aspartate receptor-mediated EPSCs with MK-801, was higher in TTX-treated than control neurons. Therefore, the activity-dependent increase in EPSC amplitude was mainly ascribed to the increase in synapse number, while activity-dependent alleviation of short-term depression was mostly ascribed to the decrease in release probability. The effect of activity blockade on short-term depression, but not EPSC amplitude, was reversed after 4 days of TTX removal, indicating that synapse number and release probability are controlled by activity in very different ways. These results demonstrate that activity regulates the conversion of immature synapses transmitting low-frequency input signals preferentially to mature synapses transmitting both low- and high-frequency signals effectively, which may be necessary for information processing in mature cortex.

PMID: 15673441 [PubMed - in process]

[bernard]

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15655256

Mol Neurobiol. 2004 Dec;30(3):341-58.

Gap junctions: their importance for the dynamics of neural circuits.

Rela L, Szczupak L.

Laboratorio de Fisiologia y Biologia Molecular, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina.

Electrical coupling through gap junctions constitutes a mode of signal transmission between neurons (electrical synaptic transmission). Originally discovered in invertebrates and in lower vertebrates, electrical synapses have recently been reported in immature and adult mammalian nervous systems. This has renewed the interest in understanding the role of electrical synapses in neural circuit function and signal processing. The present review focuses on the role of gap junctions in shaping the dynamics of neural networks by forming electrical synapses between neurons. Electrical synapses have been shown to be important elements in coincidence detection mechanisms and they can produce complex input-output functions when arranged in combination with chemical synapses. We postulate that these synapses may also be important in redefining neuronal compartments, associating anatomically distinct cellular structures into functional units. The original view of electrical synapses as static connecting elements in neural circuits has been revised and a considerable amount of evidence suggests that electrical synapses substantially affect the dynamics of neural circuits.

PMID: 15655256 [PubMed - in process]

[bernard]

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15649585

Biosystems. 2005 Jan-Mar;79(1-3):11-20.

Dynamics of pruning in simulated large-scale spiking neural networks.

Iglesias J, Eriksson J, Grize F, Tomassini M, Villa AE.

Information Systems Department, University of Lausanne, Lausanne, Switzerland; Laboratory of Neuroheuristics, University of Lausanne, Lausanne, Switzerland; Laboratory of Neurobiophysics, University Joseph-Fourier, Grenoble, France.

Massive synaptic pruning following over-growth is a general feature of mammalian brain maturation. This article studies the synaptic pruning that occurs in large networks of simulated spiking neurons in the absence of specific input patterns of activity. The evolution of connections between neurons were governed by an original bioinspired spike-timing-dependent synaptic plasticity (STDP) modification rule which included a slow decay term. The network reached a steady state with a bimodal distribution of the synaptic weights that were either incremented to the maximum value or decremented to the lowest value. After 1x10(6) time steps the final number of synapses that remained active was below 10% of the number of initially active synapses independently of network size. The synaptic modification rule did not introduce spurious biases in the geometrical distribution of the remaining active projections. The results show that, under certain conditions, the model is capable of generating spontaneously emergent cell assemblies.

PMID: 15649585 [PubMed - in process]

[bernard]

Hi Somasimplers,

The last one is an elegant paper that shows my thinking about a funnel.
A large crowd of highlighted neurons choose their best and few candidates.

For Nari:
We may view a complete neurosignature as a large tree. Branches and leaves are indispensable components of a tree but the stem support all of them and it is the real trigger/collector of them!

A tree exists because there are branches and because branches support leaves.

[nari]

Bernard

Good papers you found, but the forest fires one is a bit beyond my brain at present. Need time to work out what they are really saying.

You stated:
"A large crowd of highlighted neurons choose their best a few neurons."

This rings a bell, for after finshing Blackmore's book on memes, this is precisely what she is saying about memes. The funnel may well have a kind of a sieve in it as well, for keeping out the ones that are not useful for their healthy survival. (They do not care about the organism, only their own survival).

Neurosignatures: as with neurotags ( a term DB uses), the analogy with a tree is a good one. I am sure that as time passes, branches get lopped or break off, a bit of fertile soil does wonders for growth, and a drought may kill the tree altogether. I think about the neurosignatures in some of the PPpeople I see - they are barely able to function, let alone do anything constructive, so their neurosignature is not a positive one, it may be a very healthy, tall, wide tree. Do you see neurosignatures as being positive and negative for survival?


Nari

[bernard]

Hi Somasimplers?

Maybe some of you want some visual clues/animations? :roll:

[Diane]

Animations would be great.. don't forget the 'fungal jungle' below the surface, that exists symbiotically with the entire root system and connects the entire forest together so that messaging can happen in a big way.. I guess this would be like a digestive system for the tree, as the fungi help the tree obtain essential nutrients.
Diane

[bernard]

Diane,

It's a bit soon to create an animation!
My last posts tried to show a final scene but we have to understand/explain the previous steps. If a virtual tree is made of real ones, it needs some explaining about leaf and branches? (and fungi!).

I haven't yet explained the funnel theory, just shown it. Some more work/words before images.

[bernard]

Well,

Do not forget that these avalanches appear in small/thin slices in the paper and are seen in vivo too.

It is sure that something give an order of the avalanche (if not there'll be none!). The order/trigger is neuronal (it must be! In the actual knowledge about neurons).

The result is certainly a strong neural network with strong connections? We could take the hypothesis for a moment?!

1/ what are the state of the neurons pool activated?
It may reflect some past/present events. Some facts/evidence bring certitudes about that. These events are brought in a continuous (timeline) but discrete(?) manner. Some biologists/physiologists may say that neuron spiking is limited and it's true but we know that neurons may code/transmit their information either with neurotransmitters or directly by ions flux with gap junctions.
Thus the event may be coded with an incredible efficiency and variations. We had had in a faulty way thought that a neuron functions in a binary state, it is just true (?) for axonal information transportation. This simplicity ends with dendrites and synapses.

2/ If the neurons pool is a sequence (?), following the environment (i.e) then I may say that Nature created a 'sweet' matrix which is associating sequential and parallel processing. Nari used the 'sieve' term that fits perfectly the hypothesis!
Events are running endlessly on some neuronal level, and when needed, a sieve/funnel is activated and events simplified and stored. Events fall in the neuronal sieve and only the best are kept!

[bernard]

Hello Somasimplers,

Some more thoughts/clues.

1/ Brain is organized in a sequential and parallel manner. Some neurons are activated in sequence and some are sending/receiving information coming from associative areas.
2/ Time sequence is mandatory since impulses (Action Potential AP) are not continuous but limited in frequency then coding may be limited automatically by this constraint. A sub-system is unable to code an event with a speed that is superior to the period of the sampling frequency!
If events, APs come at 100 Hz then it is impossible to code event that are inferior of 10 ms of duration and thus brain needs absolutely to process them in a sequence or they'll be lost. A good way, in my view, is to send them in a sort of serial queue? Cortical layers seem fine candidates?

[bernard]

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15260138

Neuropsychol Rev. 2004 Mar;14(1):43-64.

Sequential memory: a developmental perspective on its relation to frontal lobe functioning.

Romine CB, Reynolds CR.

Texas A&M University, College Station, Texas 78602, USA.

The multidimensional nature of the frontal lobes serves to organize and coordinate brain functionings playing a central and pervasive role in human cognition. The executive processes implicated in complex cognition such as novel problem solving, modifying behavior as appropriate in response to changes in the environment, inhibiting prepotent or previous responses, and the implementation of schemas that organize behavior over time are believed to be mediated by the frontal regions of the brain. Overall, the functioning of the frontal lobes assists individuals in goal directed and self-regulatory behavior. Additional theories of frontal lobe functioning have focused on its involvement in temporal, or time-related domains. The organizational and strategic nature of frontal lobe functioning affects memory processes by enhancing the organization of to-be-remembered information. Among the specific memory systems presumed to be based on anterior cerebral structures is the temporal organization of memory. An essential component of memory that involves temporal organization is sequential ordering entailing the ability to judge which stimuli were seen most recently and the temporal ordering of events in memory. Focal lesion studies have demonstrated the importance of the frontal lobes on retrieval tasks in which monitoring, verification, and placement of information in temporal and spatial contexts of critical importance. Similarly, frontal lobe damage has been associated with deficits in memory for the temporal ordering, or sequencing, of events. The acquisition of abilities thought to be mediated by the frontal lobes, including sequential memory, unfolds throughout childhood, serving to condition patterns of behavior for the rest of the brain. Development of the frontal regions of the brain is known to continue through late adolescence and into early adulthood, in contrast to the earlier maturation of other cortical regions. The developmental patterns of the frontal lobes are thought to involve a hierarchical, dynamic, and multistage process.

Publication Types:

* Review


PMID: 15260138 [PubMed - indexed for MEDLINE]

[bernard]

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15190354

Nature. 2004 Jun 10;429(6992):664-7.

Temporal difference models describe higher-order learning in humans.

Seymour B, O'Doherty JP, Dayan P, Koltzenburg M, Jones AK, Dolan RJ, Friston KJ, Frackowiak RS.

Wellcome Department of Imaging Neuroscience, 12 Queen Square, London WC1N 3BG, UK. bseymour@fil.ion.ucl.ac.uk

The ability to use environmental stimuli to predict impending harm is critical for survival. Such predictions should be available as early as they are reliable. In pavlovian conditioning, chains of successively earlier predictors are studied in terms of higher-order relationships, and have inspired computational theories such as temporal difference learning. However, there is at present no adequate neurobiological account of how this learning occurs. Here, in a functional magnetic resonance imaging (fMRI) study of higher-order aversive conditioning, we describe a key computational strategy that humans use to learn predictions about pain. We show that neural activity in the ventral striatum and the anterior insula displays a marked correspondence to the signals for sequential learning predicted by temporal difference models. This result reveals a flexible aversive learning process ideally suited to the changing and uncertain nature of real-world environments. Taken with existing data on reward learning, our results suggest a critical role for the ventral striatum in integrating complex appetitive and aversive predictions to coordinate behaviour.

PMID: 15190354 [PubMed - indexed for MEDLINE]

[bernard]

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=14642461

Neuroimage. 2003 Nov;20(3):1485-92.
From will to action: sequential cerebellar contributions to voluntary movement.

Hulsmann E, Erb M, Grodd W.

Section on Experimental Magnetic Resonance of CNS, Department of Neuroradiology, University of Tubingen, Hoppe-Seyler-Strape 3, 72076 Tubingen, Germany. ErnestHuelsmann@aol.com

The cerebellum is known to be involved in numerous motor related functions, but recent observations suggest that it also performs fundamental operations on nonmotor functions such as perception and cognition. Assuming that the cerebellum has to be consulted in a limited window of time, cerebellar activation should occur in a time-dependent manner in respect to the corresponding telencephalic areas. This hypothesis was tested by combining a simple motor task with the demand of a self-paced delay using event-related functional magnetic resonance imaging. Evaluation with a time-shifted canonical hemodynamic response function revealed spatially and temporally separated cerebral and cerebellar activation accompanying the entire process--from conscious planning to final motor output--within a time frame of 6 s. The cerebral activations spread from the anterior cingulate cortex through the supplementary motor and premotor area to the primary motor and sensory cortices. This cascade was temporally in parallel with cerebellar activations propagating from the neo- to the spinocerebellum. An early lateral cerebellar recruitment 3 s prior movement onset confirms its involvement in cognitive processing. A later medial activation occurring close to movement onset most probably reflects spinocerebellar kinesthetic feedback. Between these two points a striking lateromedial succession was found, which is in line with the hypothesis of the existence of multiple internal models residing in the cerebellum, each communicating with its own corresponding telencephalic region.

Publication Types:

* Clinical Trial


PMID: 14642461 [PubMed - indexed for MEDLINE]

[bernard]

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=14527603

Neuroimage. 2003 Sep;20(1):429-34.
Temporal integration of sequential auditory events: silent period in sound pattern activates human planum temporale.

Mustovic H, Scheffler K, Di Salle F, Esposito F, Neuhoff JG, Hennig J, Seifritz E.

Department of Psychiatry, University of Basel, 4025 Basel, Switzerland.

Temporal integration is a fundamental process that the brain carries out to construct coherent percepts from serial sensory events. This process critically depends on the formation of memory traces reconciling past with present events and is particularly important in the auditory domain where sensory information is received both serially and in parallel. It has been suggested that buffers for transient auditory memory traces reside in the auditory cortex. However, previous studies investigating "echoic memory" did not distinguish between brain response to novel auditory stimulus characteristics on the level of basic sound processing and a higher level involving matching of present with stored information. Here we used functional magnetic resonance imaging in combination with a regular pattern of sounds repeated every 100 ms and deviant interspersed stimuli of 100-ms duration, which were either brief presentations of louder sounds or brief periods of silence, to probe the formation of auditory memory traces. To avoid interaction with scanner noise, the auditory stimulation sequence was implemented into the image acquisition scheme. Compared to increased loudness events, silent periods produced specific neural activation in the right planum temporale and temporoparietal junction. Our findings suggest that this area posterior to the auditory cortex plays a critical role in integrating sequential auditory events and is involved in the formation of short-term auditory memory traces. This function of the planum temporale appears to be fundamental in the segregation of simultaneous sound sources.

Publication Types:

* Clinical Trial


PMID: 14527603 [PubMed - indexed for MEDLINE]

[bernard]

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=12126657

Prog Neurobiol. 2002 Jun;67(2):85-111.
A brain perspective on language mechanisms: from discrete neuronal ensembles to serial order.

Pulvermuller F.

MRC Cognition and Brain Sciences Unit, Medical Research Council, 15 Chaucer Road, Cambridge CB2 2EF, UK. friedemann.pulvermuller@mrc-cbu.cam.ac.uk

Language is constituted by discrete building blocks, sounds and words, which can be concatenated according to serial order principles. The neurobiological organization of these building blocks, in particular words, has been illuminated by recent metabolic and neurophysiological imaging studies. When humans process words of different kinds, various sets of cortical areas have been found to become active differentially. The old concept of two language centers processing all words alike must therefore be replaced by a model according to which words are organized as discrete distributed neuron ensembles that differ in their cortical topographies. The meaning of a word, more precisely, aspects of its reference, may be crucial for determining which set of cortical areas becomes involved in its processing. Whereas the serial order of sounds constituting a word may be established by serially aligned sets of neurons called synfire chains, different mechanisms are necessary for establishing word order in sentences. The serial order of words may be organized by higher-order neuronal sets, called sequence detectors here, which are being activated by sequential excitation of neuronal sets representing words. Sets of sequence detectors are proposed to process aspects of the syntactic information contained in a sentence. Other syntactic rules can be related to general features of the dynamics of cortical activation and deactivation. These postulates about the brain mechanisms of language, which are rooted in principles known from neuroanatomy and neurophysiology, may provide a framework for theory-driven neuroscientific research on language.

Publication Types:

* Review


PMID: 12126657 [PubMed - indexed for MEDLINE]

[bernard]

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=12364499

J Neurophysiol. 2002 Oct;88(4):1695-706.
Dynamics of electrosensory feedback: short-term plasticity and inhibition in a parallel fiber pathway.

Lewis JE, Maler L.

Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada. jlewis@uottawa.ca

The dynamics of neuronal feedback pathways are generally not well understood. This is due to the complexity arising from the combined dynamics of closed-loop feedback systems and the synaptic plasticity of feedback connections. Here, we investigate the short-term synaptic dynamics underlying the parallel fiber feedback pathway to a primary electrosensory nucleus in the weakly electric fish, Apteronotus leptorhynchus. In open-loop conditions, the dynamics of this pathway arise from a monosynaptic excitatory connection and a disynaptic (feed-forward) inhibitory connection to pyramidal neurons in the electrosensory lateral line lobe (ELL). In a brain slice preparation of the ELL, we characterized the synaptic responses of pyramidal neurons to short trains of electrical stimuli delivered to the parallel fibers of the dorsal molecular layer. Stimulus trains consisted of 20 pulses, at either random intervals or constant intervals, with varying mean frequencies. With random trains, pyramidal neuron responses were well described by a single exponential function of the inter-stimulus interval-suggesting a single facilitation-like process underlies these synaptic dynamics. However, responses to periodic (constant interval) trains deviated from this simple description. Random and periodic stimulus trains delivered when the feed-forward inhibitory component of this pathway was pharmacologically blocked revealed that inhibition and depression also contribute to the observed dynamics. We formulated a simple model of the parallel fiber synaptic dynamics that provided an accurate description of our data. The model dynamics resulted from a combination of three distinct processes. Two of the processes are the classically-described synaptic facilitation and depression, and the third is a novel description of feed-forward inhibition. An analysis of this model suggests that synaptic pathways combining plasticity with feed-forward inhibition can be easily tuned to signal different types of transient stimuli and thus lead to diverse and nonintuitive filtering properties.

PMID: 12364499 [PubMed - indexed for MEDLINE]

[bernard]

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=11164022

Cognition. 2001 Apr;79(1-2):1-37.
Towards a cognitive neuroscience of consciousness: basic evidence and a workspace framework.

Dehaene S, Naccache L.

Unite INSERM 334, Service Hospitalier Frederic Joliot, CEA/DRM/DSV, 4, Place du General Leclerc, 91401 Cedex, Orsay, France. dehaene@shfj.cea.fr

This introductory chapter attempts to clarify the philosophical, empirical, and theoretical bases on which a cognitive neuroscience approach to consciousness can be founded. We isolate three major empirical observations that any theory of consciousness should incorporate, namely (1) a considerable amount of processing is possible without consciousness, (2) attention is a prerequisite of consciousness, and (3) consciousness is required for some specific cognitive tasks, including those that require durable information maintenance, novel combinations of operations, or the spontaneous generation of intentional behavior. We then propose a theoretical framework that synthesizes those facts: the hypothesis of a global neuronal workspace. This framework postulates that, at any given time, many modular cerebral networks are active in parallel and process information in an unconscious manner. An information becomes conscious, however, if the neural population that represents it is mobilized by top-down attentional amplification into a brain-scale state of coherent activity that involves many neurons distributed throughout the brain. The long-distance connectivity of these 'workspace neurons' can, when they are active for a minimal duration, make the information available to a variety of processes including perceptual categorization, long-term memorization, evaluation, and intentional action. We postulate that this global availability of information through the workspace is what we subjectively experience as a conscious state. A complete theory of consciousness should explain why some cognitive and cerebral representations can be permanently or temporarily inaccessible to consciousness, what is the range of possible conscious contents, how they map onto specific cerebral circuits, and whether a generic neuronal mechanism underlies all of them. We confront the workspace model with those issues and identify novel experimental predictions. Neurophysiological, anatomical, and brain-imaging data strongly argue for a major role of prefrontal cortex, anterior cingulate, and the areas that connect to them, in creating the postulated brain-scale workspace.

PMID: 11164022 [PubMed - indexed for MEDLINE]

[bernard]

Hi Somasimplers,

I put these papers which show, without any doubt, that brain uses sequential networks and parallel ones, at the same time. We may say that sequential networks are used to process temporal events in a queue (and maybe lost if not used?) and the parallel processes permit to coordinate information at once?

We may not forget that each event chunk is coded with a quanta of ions or neurotransmitters and give it a priority and it seems reasonable to think that high priority events have more chances to be stored than lower ones?

[bernard]

Here is my first trial about the sieve/funnel =>

the balls are a sequential event with their priorities.
A simple rule (the simplest) is applied there.

If my neighbour is weaker than me then my neighbour will be weaker.
It is a simple inhibition. If the message becomes too weak then it is not transmitted! Each ball may be represented by an action potential or a quanta of neurotransmitter but I found more understandable to use balls. You see then the weight of the stimulus and the changes more quickly?
Of course, the rules are more complex than that one but it works but slowly. Here we have a matrix with 7 columns and some rows and the process must be quicker.

http://www.somasimple.com/flash_anims/brain_avalanche.swf

flash version (http://www.somasimple.com/flash_anims/brain_avalanche.swf)
html version (http://www.somasimple.com/flash_anims/brain_avalanche_test.html)

You can enlarge the view by clicking on flash version!

[Diane]

Nice effort Bernard, you are trying to simplify the concept and make it visual.. hard work when each neuron has thousands of possible points of connection.
Diane

[bernard]

I changed the animation to a more visual one.

Here is only a plane view but more to come!