Warpspeed13 said:What would happen if you ran conductive nanowires all over the surface of the brain? For the sake of this argument we'll say that the wires are biocompatible. Would it be benificial or would it mess up the brain to have two different parts interconnected?
He awakens in a hospital where Dr. Brunder explains what's been causing his change. He has an astrocytoma brain tumor that has spread out like a hand, with threads of it everywhere. But, instead of destroying brain function, so far it has been stimulating it. Thus, George has more area of active brain use than anybody ever tested because of the tentacles from the tumor.
Pythagorean said:I agree with what others have said. It would be similar to randomly connecting the components of a complicated electrical circuit. You could cause feedback or clutter (signals that aren't supposed to be there) assuming you did it in a way that conserved signals.
Of course, there is a possibility that, given time, an organism could adapt to make use of the signals, particularly during more plastic phases of development... but you also run the risk that some circuits wouldn't develop correctly if they were receiving irrelevant signals.
atyy said:How big would the effect be, given that the brain is already bathed in cerebral spinal fluid, which is a conductor? There can be "ephaptic" electrical connectivity between neurons, but a large part of interneuronal communication is chemical, not electrical.
Pythagorean said:I would imagne something similar to axo-axonic gap junction coupling; a passive flow from the higher potential to lower potential. Though there would be some kind of capacitive coupling involved since ions can't flow through the wire.
atyy said:That's larger than what I would guess. What sort of phenomena or behaviour do axo-axonic gap junctions produce?
DiracPool said:Ephaptic coupling including electrical gap junctions are prevalent in the brain but are more of an anomaly than a selected design feature, as far as we can tell. There doesn't seem to be any conserved pattern of any type of ephaptic coupling across brain taxa that would suggest it has any specific role in sensory-motor information processing, at least.
For example, we don't consider any form of ephaptic coupling in our mathematical models of neuronal population dynamics, and I don't know of any group that does, although there might be. We've found the effects to be negligible relative to axo-dendritic electrochemical synapses, which far outweigh any anomalous ephaptic contributions. Typically, a neuron population will simply "overpower" any anomalously formed gap junction by simply producing more electrochemical axo-dendritic synapses to make up for any communication issue it may effect.
madness said:Christof Koch's group have been working on ephaptic coupling, and they would argue that it plays and important functional role in brian dynamics (e.g., http://www.nature.com/neuro/journal/v14/n2/abs/nn.2727.html). Note that this is not even gap junction coupling, it is the influence of extracellular fields on action potentials. Gap junction coupling is much stronger and can synchronise neural networks (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2744332/, http://www.jneurosci.org/content/21/15/5824.short).
madness said:Christof Koch's group have been working on ephaptic coupling, and they would argue that it plays and important functional role in brian dynamics.
There doesn't seem to be any conserved pattern of any type of ephaptic coupling across brain taxa that would suggest it has any specific role in sensory-motor information processing, at least.
atyy said:That's interesting, but with respect to the question in the OP, my guess was that what he was suggesting could be carried out by simply pouring CSF (artificial CSF, say normal saline) on the brain, since CSF is conducting, and will infiltrate the entire extracellular space. But why would pouring CSF on the brain have any effect, given that the brain is bathed in CSF already?
DiracPool said:The first article is behind a paywall, but the entirety of the articles you posted deal with ephaptic/gap junction contributions to "synchrony" of oscillations in neural tissue.
My comment was:
"There doesn't seem to be any conserved pattern of any type of ephaptic coupling across brain taxa that would suggest it has any specific role in sensory-motor information processing, at least."
And there doesn't seem to be. While gap junctions may affect and potentiate local synchrony, more global synchronies, such as thalamocortical oscillations, are regulated by the ascending reticular activating system and neurotransmitter/hormones that act through axo-dendritic synapses.
madness said:Of course synaptic and chemical mechanisms have an important effect on brain function, but that doesn't rule out a role for ephaptic coupling. .
Apart from at neuromuscular junctions and sensory organs, we don't have much direct evidence that chemical synapses play a specific role in sensory-motor processing
DiracPool said:I didn't rule out a role for ephaptic coupling, I agreed that it plays a minor role in population synchronization.
That is simply an incorrect statement. The entire dogma of neuroscience is built on the premise that chemical synapses play a specific role in sensory-motor processing. This dogma goes back 100 years to the time when Ramón y Cajal first identified the chemical synapse. The evidence for this is overwhelming. Contrarily, there is essentially zero evidence that gap junctions or ephaptic coupling is related in any way to executing complex behavioral routines or any kind of sophisticated sensory processing.
madness said:There is evidence that gap junctions execute behavioural routines http://jn.physiology.org/content/85/4/1543.short.
Our primary observations include the findings that gap-junction blockade consistently resulted in a reduction in respiratory frequency, and this occurred in both en bloc and medullary slice preparations. These results are consistent with a role of gap junctions in the generation of respiratory cycle timing. Further, in most cases, gap-junction blockade also caused a marked increase in short-time-scale synchronized activity in both phrenic and hypoglossal inspiratory bursts. This occurred in the absence of a shift in the predominant frequencies in the power spectra of this synchronized activity. In addition, we observed that gap-junction blockade caused minimal or mixed effects on the two measures we used to quantitate amplitude of inspiratory phase motoneuron activity. In contrast to the results with the gap-junction blockers, blockade of GABAA and glycine receptors caused an increase in respiratory frequency. We also found that simultaneous blockade of both of these receptors consistently resulted in a reduction in short-time-scale synchronized activity in both phrenic and hypoglossal inspiratory bursts.
The evidence for the role of chemical synapses in behaviour is no more direct or concrete than that for ephaptic coupling or gap junctions, it is just more abundant because it has been studied for longer.
DiracPool said:Show me a study that links gap junction dynamics to a behavior of even modest complexity, and not a tonic or rhythmic process.
DiracPool said:Where in there is any mention of gap junctions mediating any form of hierarchically sequenced goal-directed behavior which is the hallmark of mammalian brain function?
DiracPool said:And the way the brain works has nothing to do with what "platform" of neuronal modeling has been studied for a shorter or longer amount of time.
madness said:Show me a study which directly and causally links chemical synapses to hierarchically sequenced goal-directed behaviour.
Warpspeed13 said:What would happen if you ran conductive nanowires all over the surface of the brain? For the sake of this argument we'll say that the wires are biocompatible. Would it be benificial or would it mess up the brain to have two different parts interconnected?
atyy said:Here are more details to my earlier posts. The OP's question is about connecting the extracellular space with a conductor.
In fact this can be done by pouring artificial CSF or normal saline (0.9% NaCl) over the brain, because these are conductors and will infiltrate the extracellular space. Since the brain is already bathed in CSF, this will do essentially nothing.
However, if one changes the conductor to a solution of KCl, this will affect brain function even its electrical conductivity is similar to that of NaCl. For example, KCl can initiate cortical spreading depression.
madness said:This depends on whether the connecting wires were to penetrate the cell membranes. If they were, it would act as though the cells were connected by gap junctions, likely resulting in excessive synchronisation and seizure.
Ok so if the wires were on the surface but not puncturing the cells it wouldn't do anything?atyy said:I agree - assuming we don't puncture the cells and they all die first! Anyway, puncturing a cell typically leads to the cell depolarizing and firing action potentials, so the answer would still be correct :)
Warpspeed13 said:Ok so if the wires were on the surface but not puncturing the cells it wouldn't do anything?
Warpspeed13 said:Ok so if the wires were on the surface but not puncturing the cells it wouldn't do anything?
So if you were to have a lattice of biocompatible nano wires all over the brain and spine you could use it for a brain machine interface?atyy said:To add a bit to the post above. If you put electrodes at certain specific locations, and inject current, you can affect brain function in specific ways. For example, there is a central hearing implant that can aid lip reading, and there is deep brain stimulation for certain Parkinson's patients.
Here is an example where it seems that the electrodes eventually caused plasticity. http://www.ncbi.nlm.nih.gov/pubmed/23502431 (free link at top right).
Warpspeed13 said:So if you were to have a lattice of biocompatible nano wires all over the brain and spine you could use it for a brain machine interface?
