Medical What part of the brain is conscious?

[hypnagogue]

Hypnagogue, have you ever looked into the "defect of consciousness" that occurs in complex-partial seizures? With all this concentration on the thalamus, I just realized I'd lost sight of the non-thalamic defects of consciousness that give clues to how everything else contributes.

I've read about such things, but it's only recently that I'm making a concerted effort to form a sturdy and integrated knowledge of the anatomy of the brain and how it relates to phenomenal consciousness and various cognitive functions. I know you must've expounded on this topic a hundred times already on PF, but if you're up to it I'd be open to learning about complex-partial seizures and discussing what can be concluded from them.

 

[zoobyshoe]

I know you must've expounded on this topic a hundred times already on PF...

Actually, the subject I usually beat to death is simple-partial seizures. The "simple" refers to the fact there is no loss of consciousness, or even defect of consciousness.

but if you're up to it I'd be open to learning about complex-partial seizures and discussing what can be concluded from them.

Complex partials are the next step up in severity of effect on consciousness. The person is not unconscious, but usually in something like a sleepwalking state.

"Clearly, as the examples in this text show, these patients are not, in the ordinary sese of the word, unconscious. A patient under general anaesthesia is unconscious; however, a patient who, during a complex partial seizure, drives a car, clearly is not. In light of this, others have spoken of a `loss of contact' wherein the patient's behaviour no longer `fits' well with the environment, indicating that such a patient is out of touch.' Another proposed name for this defect of consciousness is `disturbance of contact.' However, this term seems too broad, as it could certainly include much of the symptomatology seen in illnesses such as schizophrenia. In light of this uncertainty in terminology, a return to historical roots seems prudent, and consequently in this text, Jackson's phrase `defect of consciousness' is used."

p.35

"It appears that bilateral temporal lobe involvement is required before the full symptomology of a complex partial seizure can appear. Although isolated aurae may occur secondary to seizure activity confined to one lobe, it appears that both temporal lobes must be involved before the defect of consciousness appears. Thus, when a complex partial seizure evolves out of an aura, it is generally an indication that seizure activity has spread from one temporal lobe to the contralateral temporal lobe."

p.90
Partial Seizures and Interictal Disorders
The Neuropsychiatric Elements
David P. Moore, M.D. 1997 Butterworth-Heinemann, Newton Mass. USA

A simple partial (aura) remains such so long as it is confined to one hemisphere. Once it spreads across the corpus callosum into the other hemishpere, consciousness becomes defective. As far as I know, this is accomplished simply by interrupting normal limbic, medial, and cortical functions, with no involvement of the thalamus.

This will probably not mean much until you read a good variety of case studies describing what people act like during complex partials. For the most part, they have amnesia for the whole thing after he fact, don't know what they did, and certainly can't explain what was going through their mind at the time.

Some people perseverate with whatever they were doing when the seizure started, others have a routine set of automatic behaviours. Most often you see some odd oral activity like lip smacking, chewing movements, mumbling noises, and such, which indicates involvement of the amygdala, (an organ somehow linked to oral activities, but I'm not sure how.) There is usually some residual responsiveness to the environment: a grunt of recognition at having their name called, but some people seem much more reponsive: as alert to the environment as, say, an extremely drunk person (but without the physical impairment).

That all is just a thumbnail sketch, and not enough of a foundation for a discussion. It suggests a lead to the non-thalamic necessities for consciousness. That lead could be spurious, though, were it to turn out the intralaminar nuclei are being partially affected in this situation. I've never seen mention of it though.

 

[hypnagogue]

hypnagogue, thanks much for the clarification regarding the two halves of the thalamus. I'd be curious to know just how much of the thalamus could be destroyed before consciousness no longer could be maintained. If two symetrical but small fractions of the thalamus lost function for example, would that have an effect?

The parts of the thalamus that are crucial for the maintenance of consciousness are the intralaminar nuclei (ILN), which are small groups of neurons clustered in the thalamus's laminae. (In the picture of the thalamus I posted, you can see the laminae-- they are the slender sections of tissue colored in white.) As the ILN are themselves pretty small, it doesn't take a lot of bilateral damage (damage to both sides) to cause coma. In Baars' In the Theater of Consciousness, he reports an estimate from neurosurgeon Joseph Bogen that holds that bilateral lesions to the ILN no bigger than a pencil eraser can be fatal.

The structure of consciousness is probably less sensitive to damage to other areas of the thalamus. From the link zooby posted:

NOVA: How else can consciousness get damaged?

Llinás: The other thing that can happen is that deep in the brain there is a structure called the thalamus. If the thalamus is damaged -- and this is a central entity of the brain, some sort of gateway into the brain -- if the gate is damaged then you have the same problems that you have with cortical damage. If the part of the thalamus that connects to the visual cortex is damaged then you don't see.

Recall that the thalamus has dense connections with various sensory and motor areas of the cortex. So if an area of thalamus that projects to, say, visual cortex is damaged, it stands to reason that some feature of visual consciousness will be degraded or lost. But as far as I know, the only parts of the thalamus that are really crucial to consciousness as a whole, rather than features thereof, are the tiny intralaminar nuclei. The ILN project diffusely to all areas of cortex and trigger cortical arousal, the kind of gross electrical activity that is associated with consciousness in waking states and dreaming in REM sleep. I believe the other regions of the thalamus map to dedicated areas of cortex, so damage to these areas might lead to loss of specific features of consciousness while leaving the majority intact.

Also, I might have said too much when I claimed that the two halves of the thalamus mirror each other in functionality. As far as I can tell, there does seem to be some redundancy in the function of the ILN, since consciousness can be maintained if one is damaged. However, it very well could be that the two halves of the thalamus perform somewhat different functions. I don't know enough right now to be able to say either way.

Second, would similar losses from both sides of the brain that did not include the thalamus result in some loss? In other words, assuming the brain is essentially symetrical like the thalamus, does either side perform some kind of back up to the other akin to a single failure tolerant system? The suggestion is that the thalamus is symetrical with two halves of possibly equal capability (ie: in regards to the support of consiousness). Do other parts of the brain organize themselves in similar ways? (Ex: If the brain is "single failure tolerant" with two halves of roughly equal capability, that might imply that neurons supporting the visual signals of say, the left eye, could be destroyed or otherwise rendered inoperable, without loss of vision, if (a BIG if) the opposite side of the brain was able to support those signals.)

The left and right hemispheres of the brain aren't quite mirror images. For instance, Broca's area and Wernicke's area (responsible for the production and understanding of language, respectively) are located in the left hemisphere, and in general there is evidence that the processing styles of the two hemispheres is different (the left might be more local and detail oriented, "seeing the trees," while the right might be more global and general, "seeing the forest"-- see e.g. this link).

In general, the brain features a good degree of redundancy, so in some cases it's possible to lose a fair amount of neurons without an appreciable decline in the corresponding cognitive functions. The brain also has a good degree of plasticity, especially in youth. In some cases it is possible to lose certain cognitive/motor functions and then regain them, if the remaining neural tissue can spontaneously reconnect in such a way as to carry out the lost function. I believe that in blind people, large chunks of visual cortex have been known to be 'recruited' for novel cognitive roles unrelated to vision.

But in general, I don't think the brain is constructed in such a way that loss of function on one side can be automatically taken up by the other side seemlessly. There are specialized regions all over the place whose functions aren't necessarily duplicated elsewhere. Loss of function can sometimes be compensated for by other neural tissue, but only if the relevant neurons can manage to actively rewire in a certain way.

Note that here I'm assuming a very mechanistic view of the brain in which portions of the brain crunch data and provide that output as input to a central portion of the brain which supports the conscious experience.

There isn't really one central portion of the brain where consciousness comes together. The neural systems associated with conscious experience are distributed widely across many regions of the brain.

 

[hypnagogue]

If there are portions of the brain which support consciousness, (NCC's) then one might assume a second question regards the difference between neurons, especially neurons within the thalamus and other NCC's and the nervous system in general. If there are sections of the nervous system which support consciousness, what is physically unique about them?

From what I've read, it would appear that nerve cells in general are very similar, and some with strictly dimensional differences, some with extremely long axons for example. I think I read somewhere that axons can extend essentially the length of one's leg, and axons from the thalamus can extend throughout the brain. But the clue IMHO would be to look inside to see what differences there are.

I don't yet know much about the different structures of different types of neurons, but there are different classifications for different types (see example the Crick and Koch paper to which I linked, where they show depictions of three types of neurons in the claustrum). As for the question of whether the NCC neurons have any special physical properties, I believe that is a line of inquiry in which Crick was, and Koch is, interested.

However, I strongly believe that the key feature of NCCs-- the thing that makes them NCCs at all-- is not their physical properties so much as their function. For instance, imagine gradually replacing the neurons in your brain, one by one, with tiny silicon devices, such that each replacement device performs exactly the function of the replaced neuron.

(There is the question of what level of functionality is relevant here-- the consensus for now seems to be that what is relevant is reception and transmission of electrical signals on the level of whole neurons, although some argue that processes that occur within the neurons themselves might also be important. For our purposes, we can imagine that the consensus view is correct, although if intracellular processes are important then this thought experiment could be appropriately extended to reflect that.)

(There might also arise an objection that a silicon device, or whatever, could not identically perform the relevant function of the replaced neuron. But since we are interested in dissociating function from physical structure, we can imagine that such a device exists and see what follows from our considerations.)

What happens as each neuron is replaced? If the biological properties of the NCCs are important, we might imagine that consciousness would slowly fade away or otherwise become degraded as each neuron is replaced with its artificial replacement. But since the functionality of the system as a whole would be preserved, there would be no outward manifestation of any such change. You would go on behaving as if everything were normal, reporting that you are conscious as normal, and so on, even as your consciousness was supposedly being swept out from under you! In the limit, once your brain had been entirely replaced with the little silicon devices-- assuming that the biological properties of NCCs are relevant to consciousness-- you would not be conscious at all, but would go on talking and behaving and emoting as if you were as conscious as you always had been, and you would be no less convincing in doing so.

The extreme counterintuitiveness of that scenario suggests that the physical properties of neurons are not important to consciousness, but rather, it is their functional behavior (on some level of abstraction) that makes a difference to the attendant structure and quality of consciousness. It may well be that NCCs have special physical properties relative to other types of neurons, but if this is so, it is most probably because those special physical properties enable some particular kind of functional behavior. That is, the physical properties of neurons qua physical properties are probably not relevant to conscious experience; what is relevant to consciousness is probably the particular kind of functions that neurons' physical properties enable them to carry out.

 

[hypnagogue]

Thanks zoob. I will have to do more reading and snooping around about complex partial seizures, but for now it strikes me that the effect of these seizures sounds remarkably similar to what Crick and Koch predict for loss of function of the claustrum:

What behavioural paradigms can be usefully studied using such ‘silencing’ protocols? If the claustrum were to be involved in combining information within and across modalities, it is likely that its bilateral loss would only interfere minimally with the host of sensory-motor systems that we have dubbed zombie modes (Koch & Crick 2001). That is, removing both claustra would not affect routine and stereotyped behaviours in response to some simple inputs (e.g. an eye or hand movement in response to a single, isolated visual stimulus that moves one way or another). Thus, more complex tasks may be needed to reveal loss-of-function.

The claustrum comes in two thin sheets in the general neighborhood of the temporal lobes. It might be that complex partial seizures result in 'defective' consciousness because bilateral temporal lobe epilepsy entails bilateral disturbance of the claustrum. Of course, I imagine a great many other brain regions are affected by such an episode, so some other neural system could be the real culprit. But on a coarse level, this information about complex partials does seem to dovetail pretty well with Crick's and Koch's hypothesis about the claustrum.

 

[zoobyshoe]

I'm not sure about the claustrum. I've never heard of it before this thread. As far as I know it has never been implicated in any seizure symptom. To complicate things for you, bilateral frontal lobe seizures also cause a defect of consciousness, and amnesia.

You know the whole story of how a neuron fires, don't you?

 

[hypnagogue]

The claustrum is connected to most regions of cortex, it seems, so there is a possible mechanism for many kinds of epilepsy to spread to it. Its high degree of connectivity (perhaps entailing a relative lack of differential activation or suppression with respct to wider regions of cortex), and relative obscurity in the literature, might also explain why it's not often mentioned in connection with epilepsy.

In any case, the claustrum is just proposed by Crick and Koch essentially as the binding mechanism in the brain, that neural system that coordinates various information across the brain into one coherent and unified information structure / one coherent and unified representation in consciousness. Crick and Koch's prediction for what will happen when the claustrum is disabled, then, applies equally well to what happens when the binding mechanism is disabled (whether that turns out to be the claustrum or not). So at least, this appears to be an interesting suggestion that much of the characteristic behavioral and cognitive effects of complex partial seizures ensues from disruption of the brain's binding mechanism, presumably some region of cortex or (more probably) some neural system intimately connected to the cortex.

As for how neurons fire-- I'm a bit rusty on all the particular nuts and bolts, but yes, in general I'm aware of how it happens. Ion channels, potential differentials, influx of ions down the length of the axon to create electrical pulses, neurotransmitters at the synpases, spontaneous firing rates and so on.

 

[zoobyshoe]

The claustrum is connected to most regions of cortex, it seems, so there is a possible mechanism for many kinds of epilepsy to spread to it.

Just googled "claustrum + seizures" and found this:

Susceptibility to Kindling and Neuronal Connections of the Anterior Claustrum -- Zhang et al. 21 (10): 3674 -- Journal of Neuroscience
Address:http://www.jneurosci.org/cgi/content/abstract/21/10/3674

influx of ions down the length of the axon to create electrical pulses...

What's important to bear in mind is that these aren't "electrical signals" in the way we normally think of electricity at all. This is a whole different ball of wax than normal current in a conductor. It is more akin to the discharge of an extremely elaborate capacitor, and one that is highly unusual in that the potential is created by separating a higher degree of positive charge from a lower one. The outside of the neuron is switching from more positive to less positive. If a neuron cocks and discharges 4 times a second we might think of it as blinking: an alternately expanding and contracting positive electric field.

That is important because seizure activity demonstrates that all neurons in the vicinity are affected by any neuron which happens to be misfiring by simple electric induction: no synaptic connections necessary.

A seizing neuron fires, among other things more forcefully than normal, and it is the greater electrical field it produces that entrains the susceptible neurons around it into the same, abnormally strong firing pattern. The more that are entrained, the more that can be entrained. And of course the firing pattern is transmitted through normal synaptic routes, as well, to neurons "down the line."

The thing to take away from this is that normal neurons almost certainly also "sence" the neurons around them firing, by induction, without being entrained into firing themselves. Neurons as transmitters of impulses from one location to another may be overrated in importance, and their capacity to create "blinking" electric fields underrated. We have to look at EVERYTHING* that happens when neurons fire before we can figure out what's what.

*I've been reading too many posts by ZapperZ

 

[Q_Goest]

zoobyshoe said: Ramachandran is a flashy showman, and I was wondering what you might make of his discovery that squirting water in the ears of the "denial" stroke patients seemed to cause their awareness of their condition to come into full focus.

For simplicity, I'll quote that section here:

In Ramachandran's view, the struggle is between the brain's hemispheres. When isolated facts are reported which might upset the mind's currently held view of the world, the reaction of the left hemisphere is to ignore them. Most of the time, this will be the correct response; sensory systems are not perfect. But the right hemisphere carries out the occasional reality check, just to be sure, and if it thinks something's awry, it gets together with the left hemisphere and, quite literally, changes the mind. In stroke patients who cannot recognise their condition this mechanism stops working. The right hemisphere messages never get through and then, he says, "There is no limit to the delusions that the left hemisphere will engage in."

The condition is not permanent. Though it will reassert itself, it can be dissipated for a few moments by squirting ice-cold water into the ear on the unparalysed side. The effect is easy to miss, because if you squirt cold water into the wrong ear, as Dr Ramachandran did the first time he tried it, you are left with a patient who is confused, and angry that anyone should have squirted cold water without warning or reason into her ear, but still unaware that she is paralysed. But if the water is squirted into the ear of the damaged hemisphere the patient experiences a period of confusion and then about ten minutes when she knows perfectly well that she has been paralysed - cannot imagine not knowing this, in fact. Six hours later, she will have forgotten the whole episode, and once more be convinced that everything is working properly.

From the NOVA article comes this:

Maybe in the very primitive animals, in which cells did not have a single systemic property -- in which each cell was a little island, if you wish -- there may not have been consciousness, just primitive sensation, or irritability, and primitive movement. But as soon as cells talked to one another there would be a consensus. This is basically what consciousness is about -- putting all this relevant stuff there is outside one's head inside, making an image with it, and deciding what to do. In order to make a decision you have to have a consensus.

Point being, I've heard it said that the brain operates akin to a voting operation wherein each neuron 'votes' per se (NCC's only vote?) and majority rules. So is the stimulation in the ear 1) forcing neurons to vote more strongly, or 2) somehow able to get the neurons to find a path around the block created by the stroke, or 3) something else? I wonder if there is any evidence that the isolated side of the brain 'goes to sleep' so to speak, after a stroke and the ice water functions like an alarm clock. Or is there actually an information road block set up in the brain?

This is all interesting and mysterious, and it may have something to do with how neurons create consciousness, but it doesn't seem to lend much help other than with some 'easy' problems. Voting does not help with the binding problem IMO, any more than voting for George Bush gives people a sensation of unity, which is to say it doesn't. It does however, seem to indicate what the brain is doing, and may be considered circumstantial evidence for the voting analogy.

Regardless of this voting analogy, I think the more striking finding seems obvious. How is it that in these stroke victums, where parts of their brain are no longer getting signals through to each other, are these signals getting through during this temporary period when ice water is put into the ear? If connections are severed, how is it they are 'reconnected' temporarily? Are there other pathways around the block? And if there are, why doesn't the brain use them all the time? If it doesn't use them, then why doesn't the brain have two separate sensations of consciousness, because if there is a block inside the brain which prevents the flow of information, why is each half not conscious and aware of different information like someone with schizophrenia?

I think I'll suggest this experiment be performed on my mother. She's had a few mini strokes and has a bad memory now. Perhaps a little ice water in the ear will help!

 

[zoobyshoe]

The squirting of water in the ear demonstrates that the so called "denial" was not psychological, but neurological. How the squirting of cold water in the ear on the damaged side of the brain works to clear up the misinformation isn't clear. Ramachandran doesn't even suggest how it might be working.

The point is, I don't believe it would work on an alcoholic who is in denial about having an addiction to alcohol. These patients aren't denying their condition because it's too hard to face. The damage itself is creating an unusual situation where imput to adjacent, non-damaged areas continues from within the brain, and not from the affected side of the body. The problem isn't a blocking of information to consciousness at all, but, as you put it before, a feeding of misinformation to consciousness.

Their motor control is gone: they can't move their muscles, but some of the sensory controls are intact, and more importantly, their proprioception is intact: the sense of body position. They develop phantom limbs, or rather, a whole phantom side of the body, without having lost the physical original.

------

Very sorry to hear about your mother.

Memory problems, for the most part, result from interference with an important part of the limbic system called the hippocampus. This is an organ whose proper functioning is a vital to the creation and retrieval of memories as the thalamus is to consciousness.

The hippocampi (there are two, actually, one on each side, which touch each other in the middle, like the two thalami) are so called because some early anatomist thought they looked like seahorses, which is what "hippocampus" means. Really, though, they only have the same basic curl as a seahorse.

The two amygdali are mounted on the very end of the hippocampi and directly moderate their functioning. Any disconnect, or interference of the communication of the amygdala with the hippocamus, can cause strange disturbances of memory, or the hippocampus can be affected alone, also preventing the proper creation and retrieval of memories. "amygdala" means "almond", and again, this is because its shape suggested that nut to some early anatomist.

I am mostly interested in seizures and haven't researched the means by which strokes affect the hippocampus, directly or indirectly, but I've heard memory problems oftem mentioned in conjunction with strokes. Any loss of circulation to the temporal lobes in general would affect memory along with many other things.

 

[Burnsys]

You must see this video:

http://www.elrellano.net/videos/videofiles/perro-furioso.zip

It's a dog who seem to not reconozige his own leg, even to the point of biteing it.

Don't worry, has no virus, just a video

 

[Johann]

How is it that in these stroke victums, where parts of their brain are no longer getting signals through to each other, are these signals getting through during this temporary period when ice water is put into the ear? If connections are severed, how is it they are 'reconnected' temporarily? Are there other pathways around the block?

I am somewhat baffled as to why it doesn't seem to occur to neurologists that electrical signals can travel through empty space. Of course when you have a physical connection with low electrical resistance radiation can't play a significant part, but when the connection is severed it seems quite possible, at least in principle, that some form of weak communication between neurons still occurs.

The interesting thing about this hypothesis is that it would explain a lot of so-called psi phenomena by purely natural means, instead of simply denying their occurrence on the basis of our inability to account for them.

And if there are, why doesn't the brain use them all the time?

If my hypothesis is correct, the reason radiation doesn't play an important part most of the time is the same reason channel 3 disappears from your TV when you hook up the VCR. But as soon as you disconnect the VCR cable, a ghostly image of channel 3 suddenly appears, even without an antenna.

why doesn't the brain have two separate sensations of consciousness, because if there is a block inside the brain which prevents the flow of information, why is each half not conscious and aware of different information like someone with schizophrenia?

Actually, there are many documented cases of split consciousness, in which half of a person doesn't know what the other half is doing.

 

[Q_Goest]

I am somewhat baffled as to why it doesn't seem to occur to neurologists that electrical signals can travel through empty space.

But in the brain, the means of communication, at least between neurons, is the transfer of ions across the synaptic gap. In that case, I don't think electromagnetic radiation is going to do anything.

Perhaps the neuron has something inside going on (inside the cell wall) that may interact with an electromagnetic field, though I have to believe this has been looked at. Maybe someone here knows.

Regarding electromagnetic pulses in the brain, I've been looking also into brain waves. Not sure exactly what these are. Are these electromagnetic fields in the brain and somehow supported by neurons or are they the firing of neurons in a wave like fashion (ie: neurons emitting and receiving ions in phase - similar to "the wave" created where people stand up and sit down in a large stadium) or something else? I have to wonder how these brain waves are set up. What initiates them and how they are controlled? They seem to have a lot to do with conscious experience.

 

[Johann]

But in the brain, the means of communication, at least between neurons, is the transfer of ions across the synaptic gap. In that case, I don't think electromagnetic radiation is going to do anything.

That depends on the frequency of the electromagnetic signal. Frequencies from x-rays and above have enough energy to cause ionization.

Perhaps the neuron has something inside going on (inside the cell wall) that may interact with an electromagnetic field, though I have to believe this has been looked at.

If the frequency required is in the order of x-rays I suspect it would be impossible to carry out experiments. I can't imagine a researcher aiming an x-ray gun into a subject's head to test if they go bananas. At best this can only be an untestable hypothesis, but it may explain some things we currently don't understand.

I had this idea because I saw too many so-called mediums do things that cannot be explained as coincidences. Most mediums are charlatans (especially the popular ones), but a few of them do have some very strange abilities. However, I never heard of a medium who could tell things a person didn't already know, and that got me thinking that perhaps encoded EM signals play a major part in brain activity. If that were true, mediums would simply have the ability to "read minds" by tuning to signals coming from other people's brains.

Regarding electromagnetic pulses in the brain, I've been looking also into brain waves. Not sure exactly what these are.

As far as I know nobody knows what they are, except that they strongly correlate to specific states of consciousness.

Are these electromagnetic fields in the brain and somehow supported by neurons or are they the firing of neurons in a wave like fashion (ie: neurons emitting and receiving ions in phase - similar to "the wave" created where people stand up and sit down in a large stadium) or something else?

I think they are not similar to waves created by crowds as the speed of transfer from one neuron to another is too low. This might be another case in which sensitivity to low-intensity, high-frequency EM signals may be involved. But I'm speculating.

They seem to have a lot to do with conscious experience.

They do to the extent that the states of wakefulness and sleeping are associated with different frequencies. But nobody knows why.

 

[zoobyshoe]

Brainwaves, as read on the surface, are just the sum total of all the neuronal activity going on at the time in the vicinity of a given scalp electrode. It takes something like a million neurons firing to register a response on an electrode.

Electromagnetic waves do, indeed, affect consciousness. They don't have to be anywhere near x-ray frequency (which is just plain damaging). Normal solenoids pulsing at 15 hz placed right against the head can cause strange dreamy states of mind. A Canadian researcher named Michael Persinger has been experimenting with this for years. You can google his name for articles about him, and lists of his research papers.

 

[Johann]

Brainwaves, as read on the surface, are just the sum total of all the neuronal activity going on at the time in the vicinity of a given scalp electrode. It takes something like a million neurons firing to register a response on an electrode.

I don't think there's any mystery concerning the source of electrical signals in our scalp. What nobody seems to know is what those signals mean. At least that is what two neurologists told me after taking my EEG. They basically said something like, "we measure this stuff and we know certain patterns are associated with certain conditions, but we have no clue why".

Electromagnetic waves do, indeed, affect consciousness. Normal solenoids pulsing at 15 hz placed right against the head can cause strange dreamy states of mind. A Canadian researcher named Michael Persinger has been experimenting with this for years.

How could I have forgotten that? I did read about Persinger's research a few years ago. I remember one experiment in which he induced an alien-abduction experience in a subject by applying EM fields over his head and waving a flashlight in front of his eyes. It was a funny story because Persinger claimed to have found the explanation why people have those experiences, and then a skeptic asked him: "that is a fine explanation Dr. Persinger, but when someone is having the experience of being abducted by an alien, who do you think is waving the flashlight?"

In any case, 15 Hz is too low a frequency to be used for inter-neuron communication so it isn't really what I had in mind. It would be interesting to know if neurons emit EM signals whose frequency is high enough to propagate across the brain or even beyond the skull.

 

[Q_Goest]

Out on a limb?

I realize I'm going way out on a limb in suggesting this, but thought it was interesting to ponder nevertheless.

In the December 23/30 issue of Nature, M. S. Dresselhaus provided an article regarding some work done by Wang et al.

In Applied Physics Letters, Wan et al. show in a clear way that an array of aligned carbon nanotubes cane behave as an electromagnetic antenna.

The actual article is online at Applied Physics Letters.

There is also a nicely written, brief and concise review of that letter and similar work here at http://scienceweek.com/2005/sb050204-2.htm

Here's the thought: Microtubules in cells are similar in structure to nanotubes. If nanotubes can act as antennas, could microtubules do the same thing?

I understand microtubules can also be found in plant cells, so I'm not suggesting microtubules are the cause of consciousness, but rather, could it be they are necessary for function?

 

[Johann]

I realize I'm going way out on a limb in suggesting this, but thought it was interesting to ponder nevertheless.

Don't worry about going out on a limb; you are welcome here

I understand microtubules can also be found in plant cells, so I'm not suggesting microtubules are the cause of consciousness, but rather, could it be they are necessary for function?

You mean microtubules as in Roger Penrose's microtubules? There's a whole debate on that already, although the focus is on quantum mechanics, not electromagnetism.

All in all, I think there must be some organizing force acting simultaneously on the whole brain; it's the only thing that can explain how billions of neurons can work together without creating absolute chaos. As far as I can tell, electromagnetic radiation is the most likely candidate, since we already know neurons respond too slowly to electrical impulses. It's a hypothesis that is very difficult to investigate, but it can certainly be entertained by amateur neuroscientists.

 

[hypnagogue]

Point being, I've heard it said that the brain operates akin to a voting operation wherein each neuron 'votes' per se (NCC's only vote?) and majority rules.

It's certainly not the case that only NCCs 'vote.' The influence of unconscious cognitive processes is ubiquitous, even in those processes that wind up finding representation in consciousness. What you experience in consciousness is only a kind of surface representation of what is going on in your brain, a kind of a tip of the iceberg. All the while there is an enormous amount of unconscious activity going on, some of which always remains unconscious, some of which can potentially find expression in conscious experience, and some of which helps to shape the character of conscious experience despite never actually being experienced.

 

[hypnagogue]

But in the brain, the means of communication, at least between neurons, is the transfer of ions across the synaptic gap.

Actually, neurons commuicate across the synaptic gap by means of neurotransmitters, not ions. The role that ions play in neural communication is that the systematic flux of ions into and out of a neuron is what causes a kind of electrical charge to travel down a neuron's axon. There's a nice explanation of this process on the web here.

 

[hypnagogue]

All in all, I think there must be some organizing force acting simultaneously on the whole brain; it's the only thing that can explain how billions of neurons can work together without creating absolute chaos. As far as I can tell, electromagnetic radiation is the most likely candidate, since we already know neurons respond too slowly to electrical impulses. It's a hypothesis that is very difficult to investigate, but it can certainly be entertained by amateur neuroscientists.

There are several general mechanisms by which the brain's activation patterns are coordinated and organized. Regular pulses of neural signals sent widely across the brain (I believe originating from the brain stem) act as a sort of timing device that helps keep individual neurons and neuron groups coordinated. The brain also features rich re-entrant feedback loops which help to stabilize, magnify, and propogate certain neural signals. There may be other such mechanisms; without looking up any specific information, this is the best I can offer right now, off the top of my head.

 

[zoobyshoe]

I don't think there's any mystery concerning the source of electrical signals in our scalp. What nobody seems to know is what those signals mean. At least that is what two neurologists told me after taking my EEG. They basically said something like, "we measure this stuff and we know certain patterns are associated with certain conditions, but we have no clue why".

The average neurologist may not be up on this research, but I bet if you looked through medical journals you'd find they have all kinds of good leads.

(Any neurologist who is in the process of treating you is probably the worst person to ask general questions about neurology. They don't have time to give any explanations that take more than a couple sentences, and will avoid going into it.)

"that is a fine explanation Dr. Persinger, but when someone is having the experience of being abducted by an alien, who do you think is waving the flashlight?"

Whatever bright star or airplane the person became fixated on would serve as the flashlight. The article I read in Omni magazine many years ago said he got the "Alien Abduction" scenario simply by suggesting to the subject that he was staring at a bright light in the sky (no flashlight used).

In any case, 15 Hz is too low a frequency to be used for inter-neuron communication so it isn't really what I had in mind.

Why is 15 hz too low a frequency?

It would be interesting to know if neurons emit EM signals whose frequency is high enough to propagate across the brain or even beyond the skull.

The frequency would have little to do with it. It's the strength of the signal that determines how far it can propagate. The strength of the signal is the product of how many neurons are firing at the same time. As I mentioned earlier, it takes about a million neurons firing at once to be picked up through the scull by a surface electrode, and these have to be firing more or less on the surface of the brain.

The EM wave produced by a firing neuron in unbelievably weak. During seizures, as I mentioned in an earlier post, an individual neuron fires more strongly than otherwise. In this case it can cause surrounding neurons (ones right next to it) to go off by mere induction, and things can cascade from there. This is different than one neuron setting the next one off by neurotransmitters across the synapses.

Persinger's solenoids are almost certainly setting neurons off by induction, and there is probably secondary neurotransmitter communication from there.

Over what distance are neuronal EM waves effective? Can the left hemisphere of a split brain patient pick up what is going on in the right hemisphere by induction? There doesn't seem to be any indication that it can. Persinger's solenoids give off an extremely strong EM signal compared to anything the brain itself can produce, which probably accounts for the large-scale effects they can have.

Anyway, the stroke patients who don't seem to realize they are half paralyzed aren't suffering from "blocks" that can be bridged in the way Q-Goest was speculating. The parts of their brain which might process the information into knowledge they are paralyzed are receiving contradictory imput which it seems to be resolving by "trusting" the feeling that the paralyzed limbs are still moving and active over the visual information that they aren't. Information isn't being blocked by any physical damage to connections here. Certain circuits are electing to go to sleep, so to speak, and not process it, in order to keep the whole picture more or less coherent.

 

[Q_Goest]

You mean microtubules as in Roger Penrose's microtubules? There's a whole debate on that already, although the focus is on quantum mechanics, not electromagnetism.

Actually, I believe we have to give Stuart Hameroff the credit for coming up with that one.

Yes, his idea regards quantum mechanical processes in the brain, but let's disregard that possibility for a moment. The concept may or may not be proven. What I was suggesting was the possibility that microtubules could act as transmitter/recievers for neurons like miniture radio stations. If this were true, that might predict there are electromagnetic fields within the brain that correspond to the information about which we are consciously aware. The neurons might be calculating things across synaptic gaps, but the neuron might have a secondary reaction to the electromagnetic field which might serve as a 'canvas' of information we are aware of.

Would it be possible that the brain processes information in more than one way, and the way in which the information is processed results in either conscious or subconscious awareness of that information? I think the unique idea here is that perhaps there are two methods of interpreting information by the brain.

 

[Q_Goest]

It's certainly not the case that only NCCs 'vote.'

Thanks for the clarification. I was always under the assumption that all neurons have some threshold, below which they don't 'fire' and above which they do. Is that a correct way of percieving a neuron's function? How could that be better explained?

 

[Q_Goest]

Actually, neurons commuicate across the synaptic gap by means of neurotransmitters, not ions.

Thanks for the clarification. I'll have to look into neurotransmitters a bit more now.

 

[hypnagogue]

Thanks for the clarification. I was always under the assumption that all neurons have some threshold, below which they don't 'fire' and above which they do. Is that a correct way of percieving a neuron's function? How could that be better explained?

Yes, that is quite true. Neurons normally have a resting potential, such that the interior of the neuron is negatively charged with respect to the exterior. A neuron's potential can be be made either more or less negative by inputs it receives from other neurons at its dendrites. If the inputs a neuron receives raise its potential above a certain threshold, then the action potential (process of neural firing) is automatically triggered. (Actually, neurons normally fire spontaneously at some rate; inputs from other neurons can make a given neuron fire more or less rapidly, though.) Here are some good links that go into further detail:

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/E/ExcitableCells.html
http://www.everything2.com/index.pl?node=neuron

However, the threshold of a neuron's action potential is just about the mechanics of individual neurons. This threshold is not to be confused with e.g. some notion of a threshold that might obtain between neural events that find expression in consciousness and those that don't. All neurons function in the same basic manner with voltage thresholds and action potentials and the like, but of course, not all neurons directly contribute to conscious experience.

 

[somasimple]

HI,

Actually, neurons commuicate across the synaptic gap by means of neurotransmitters, not ions.

It is certainly true for a little population of peripheral neurons but false for 80% of brain ones that use gap junctions. A gap junction is a direct connection that transmit a ion flow from a neuron to another.

The transmission of action potential is not electrical but ionic since ions cross the membrane through ion channels. If it was electrical you will have a huge problem to solve: the soliton wave (the traveling action potential) rejects an electrical explanation

There is so many balloneys/contradictions about neurons.

 

[somasimple]

About NCC, it seems that it is an old thing located in the brainsteem for some scientist (Damasio) and thalamus for some other.

Do not forget that cortices are projections of older sites and may override their behaviours.

 

[zoobyshoe]

The transmission of action potential is not electrical but ionic since ions cross the membrane through ion channels.

Yes, this is important to realize. Terms like "the electrical activity of the brain" have mislead people into assuming too many incorrect comparisons with elecrical circuits.

 

[somasimple]

Yes, this is important to realize. Terms like "the electrical activity of the brain" have mislead people into assuming too many incorrect comparisons with elecrical circuits.

I would like that neuroscientists and neurophysiologists heard this. They are glued with a 75 year old cable theory and push their researches in the wrong direction. Neuron is a fabulous and simple cell.

 

[selfAdjoint]

I would like that neuroscientists and neurophysiologists heard this. They are glued with a 75 year old cable theory and push their researches in the wrong direction. Neuron is a fabulous and simple cell.

Actually models derived from cable theory work pretty well in predicting the responses of the dendrites, those often overlooked "other processes" of the neuron. It's not just all about axons.

 

[somasimple]

Hi,

A mathematical model is just a mathematical model that mimics Nature. But it remains only a curve fitting IMHO. The cable model isn't reliable for:

ions that cross membrane
continuity
travelling wave
latency time
refractory period
saltatory conduction
amplification of AP seen in dendrites
acceleration AP seen in "trees"

Well, quite 99% of a neuron functioning.