What part of the brain is conscious?

[hypnagogue]

Without explaining that damage to the reticular formation, or its communication to the intralaminar nuclei, causes coma by interrupting the functioning of the thalamo-cortical complex there is an implication that at least two separate areas exist where consciousness is developed, analagous, perhaps to the two language areas.

There is no such implication so long as we understand the word "necessary" properly. In the same post where I copied that quote from Baars, I also pointed out that necessary conditions are not the most important thing to consider in the search for NCCs. I pointed out that a functional heart is a necessary condition for consciousness too, even though the heart should not be taken to be a correlate of consciousness-- there is certainly no implication that the heart is an area where consciousness is "developed" or anything like that, even though it is necessary for consciousness.

To state it again, this time without using formal logic: Necessary conditions can be thought of as enabling conditions. If X is necessary for Y, then Y cannot exist without X, but that doesn't entail that X is crucial for Y in any way beyond providing some sort of enabling role. For instance, in order to create a painting, it is necessary to have some sort of surface on which to paint. (I'll use the word 'canvas' to refer to any such surface.) Without a canvas, there can be no painting-- the canvas presents a kind of condition that enables the possibility of creating a painting. Still, it doesn't follow that merely being in possession of a canvas entails the existence of a painting.

Furthermore, if we say something like "a canvas is a necessary condition for the existence of a painting," we do not have to qualify this statement by saying something like "however, a canvas is only important insofar as it absorbs brush strokes, which is when the painting is really created." Such a qualification amounts to saying "the canvas is necessary, but not sufficient, for the existence of a painting." But we've already established that the canvas is necessary for the painting, and have not stated or implied anywhere that it is sufficient-- the question of its sufficiency is left open. So while it is helpful to specify that it is indeed not sufficient, it's not as if we need to come out and specify this in order to correct an error inherent in the original claim. Necessity does not imply sufficiency in any way at all.

If X is sufficient for Y, then the existence of X guarantees the concomitant existence of Y. It should be clear, then, that in the search for NCCs, we are interested in those neural systems whose activity is sufficient for consciousness-- we want to find those neural systems such that, whenever they function in a certain way, it is guaranteed that some feature of consciousness exists. In the painting example, certain kinds of brush strokes on a canvas would present sufficient conditions for the existence of a painting. So when we talk about what brings a painting into existence, what we're really interested in is the brush strokes. At the same time, we recognize the necessity of the canvas in order to enable those brush strokes to occur. We can say that, assuming we are given a canvas on which to paint, certain brush strokes are sufficient for the creation of a painting.

This squares pretty straightforwardly with Chalmers' definition of an NCC:

An NCC is a minimal neural system N such that there is a mapping from states of N to states of consciousness, where a given state of N is sufficient, under conditions C, for the corresponding state of consciousness.

The NCC is what presents sufficient conditions for consciousness, so that's what we're really interested in. At the same time, we recognize the necessity of certain other conditions to hold in order to enable these NCCs to be sufficient for consciousness. These necessary conditions are the background conditions C. The reticular formation and intralaminar nuclei are probably two neural systems included in C.

I was mainly responding to your comment that "damage to the thalamus results in coma, which is not true of any other part of the brain." Essentially, this amounts to saying that the thalamus is the only brain region whose proper functioning is necessary for consciousness.

Maybe and/or no, depending. I'm trying to convey my sense of the importance of the thalamus to consciousness without making any choices about what else might also be necessary.

You already did make such an implicit choice in the statement I quoted. If N is necessary for consciousness, then without N, consciousness cannot exist (by definition of "necessary"). In other words, if N is necessary for consciousness, then if N is substantially damaged, coma follows. The converse is also true: If N is substantially damaged and coma follows, then N must be necessary for consciousness. Thus, if the thalamus is the only brain region whose damage entails coma, then it follows that the thalamus is the only brain region that is necessary for consciousness. You claimed that the thalamus is indeed the only brain region whose damage entails coma, which is equivalent to saying that the thalamus is the only brain region that is necessary for consciousness. (Of course, we know there is at least one other neural system that is necessary for consciousness, the reticular formation.)

A thalamus in a vat would, almost certainly, not constitute a proper consciousness.

I agree. But if this is true, it follows that damaging every part of the brain but the thalamus would lead to coma (assuming the body is put on life support to prevent outright death). This contradicts the claim that the thalamus is the only part of the brain whose proper functioning is necessary for consciousness.

(sotto voce: This, though, already bothers me. Speaking of the connection as a "correlate" suggests that the coiner of the term is operating with a "ghost in the machine" notion in the background.)

I see absolutely no reason why this should bother you. It seems that the neutrality of the term "correlate" bothers you because it merely admits of the possibility of certain views on consciousness, and that in turn should only bother you if you think you already know the nature of the causal relationship between brain and consciousness with certainty. I hope that's not the case, because frankly, no one does right now.

The neutrality of the term itself certainly doesn't suggest one view or another-- how could it? It's neutral! The whole point is that we should be able to focus on the (relatively!) straightforward, empirical issue of what brain regions are related to what features of consciousness without getting bogged down in complicated, contentious, and ongoing theoretical arguments about the causal nature of that relation. The idea is to treat the data purely, as data, and leave the heavier theoretical stuff for other discussions. This can only be a good thing, as it clarifies and simplifies the empirical program.

And if you still don't trust the term on the unfortunate suspicion that it's being used for malicious philosophical purposes, consider the http://www.absoluteastronomy.com/encyclopedia/n/ne/neural_correlate_of_consciousness.htm : "The neural correlate of consciousness (NCC) is a term made popular by Francis Crick and Christof Koch in the early 1990s." Unless you think the inimitable scientist Crick has a volume of "ghost in the machine" literature to be published posthumously (perhaps currently in press), I think your concern here can be put to rest.

Chalmers must obviously have laid out a working definition of consciousness such that he can determine when sufficent conditions have been met. I've been trying to avoid getting into this can of worms, because I can't imagine there would be no challenges to his working definition.

Chalmers' paper merely clarifies what is meant by "NCC" (drawing heavily from how the term has been used in the scientific literature) and discusses some issues related to the scientific search for NCCs. The determination of what conditions are sufficient for consciousness is not some a priori matter of which Chalmers has constructed his own idiosynchratic version-- that is something that obviously must be discovered empirically.

To be honest, I am somewhat frustrated that you refuse to read the paper because of a preconceived notion of what the paper must be like, apparently based on the author. As I've said, the topic of NCCs is largely theory-neutral by definition, so it should stand to reason that Chalmers' own theories on the nature of the causal relation between the brain and consciousness do not figure into his discussion of NCCs. It is precisely because we are talking about the neural correlates of consciousness that the can of worms you fear does not rear its head.

To drive this point home, here again is the general definition of an NCC at which Chalmers arrives:

An NCC is a minimal neural system N such that there is a mapping from states of N to states of consciousness, where a given state of N is sufficient, under conditions C, for the corresponding state of consciousness.

He also offers a more specific definition for neural correlates of contents of consciousness:

An NCC (for content) is a minimal neural representational system N such that representation of a content in N is sufficient, under conditions C, for representation of that content in consciousness.

Now consider http://www.klab.caltech.edu/~koch/Elsevier-NCC.html . Some selected quotes from the Crick and Koch paper:

"It is important to distinguish the general, enabling factors in the brain that are needed for any form of consciousness to occur from modulating ones that can up- or down-regulate the level of arousal, attention and awareness and from the specific factors responsible for a particular content of consciousness." (the enabling factors are the 'conditions C' in Chalmers' definition)

"The question motivating much of the current research into the neuronal basis of consciousness is the notion of the minimal neural activity that is sufficient to cause a specific conscious percept or memory."

"The specific processes that correlate with the current content of consciousness are referred to as the neuronal correlate of consciousness, or as the NCC. Whenever some information is represented in the NCC it is represented in consciousness." (note how this squares with Chalmers' definition of an NCC for contents of consciousness)

"The NCC is the minimal (minimal, since it is known that the entire brain is sufficient to give rise to consciousness) set of neurons, most likely distributed throughout certain cortical and subcortical areas, whose firing directly correlates with the perception of the subject at the time. Conversely, stimulating these neurons in the right manner with some yet unheard of technology should give rise to the same perception as before." ('direct correlation' and 'stimulating NCC neurons leads to some conscious percept' are different ways of talking about sufficiency)

The whole large meal thing is pretty much baffling to me, because shouldn't the quest be to find the minimum amount of food that will be sufficient for the hungry person to say "I am no longer hungry?" The kinds of things you used in your example as "superfluous" don't strike me as on the mark for a good analogy. Wouldn't "superfluous" be any amount of food in excess of that which satisfies his hunger, rather than things like trays and trips to tibet?

The degree to which one's hunger is satiated is a function of how much food one eats. If I would have constructed the analogy as you suggested, that would imply that all neural systems can present sufficient conditions for consciousness, if only they are somehow activated enough, or in the right manner. But as far as we know, that is not the case. There are plenty of unconscious neural mechanisms whose activity is never represented in consciousness under any circumstances.

For instance, consider the neural mechanism that guides the fine, complex, low level motor movements we make when we walk. We never have direct conscious access to the internal workings of this mechanism, and its functioning is never directly represented in all its gory detail in conscious awareness. If eating is to hunger satiation as (say) activity in the thalamus is to consciousness, then the brain's 'walking mechanism' is like watching TV. Its functioning is completely irrelevant to consciousness. Nonetheless, if it is true that the thalamus presents sufficient conditions for the existence of consciousness, it is also true that the thalamus and the 'walking mechanism,' taken together, are also sufficient for consciousness. But since the 'walking mechanism' is basically irrelevant to consciousness, we are not interested in it and want to strike it from the NCC records. We do this by looking for the minimally sufficient conditions for consciousness, those sufficient conditions for consciousness that do not include anything superfluous.

 

[zoobyshoe]

To be honest, I am somewhat frustrated...

I sense this in your whole post, and I think the conflict is one of method of approach. You are deeply immersed in a very structured, formal approach, and are not understanding why I'm not quick to adopt the same.

The formal discipline of logic is important for you because you are young, and planning to continue your formal education in this field. You are going to need to be able to speak about just about everything in logic terms. I am 50, and might only run into situations where it would be of use here and there, and only at PF. It's too much work to learn just to be able to engage in certain kinds of, for me, isolated discussions. Plus, I know you're fully capable of talking about all this at my level. I read a book here, a study there, talk to mentally ill people, people with brain damage, people with seizures. people with MS, and so forth, and, I believe, end up understanding quite a bit about the brain without also being able to state things in formal logic terms.

The majority of people I post to about the brain aren't trained in formal logic, and would lose interest in what I had to say if I translated things into those terms. It's hard enough, sometimes, maintaining their interest once you start using unfamiliar words like hippocampus, amygdala, parahippocampal gyrus, and such.

Also, I'm not resisting reading the Chalmers for any other reason than that it sounds like complex reading: new terms and new concepts to grasp and get used to. I don't recall ever hearing of him before this thread, and also don't know who Crick is, or any other name you've mentioned. I admit I may be wrong about the implications I read into the word "correlate" but that isn't why I haven't read it yet at all.

 

[hypnagogue]

Sorry if I read too much into your reply. I do think it's important to maintain some level of logical rigor when talking about somewhat complex subjects like this, though. For the purposes of this thread, formal logic isn't needed-- I just brought it up to try to illustrate a point with more clarity. However, it is important to distinguish between necessary and sufficient conditions, but I don't think that's too demanding.

btw, surely you know Francis Crick? Of Watson and Crick fame, discoverers of the structure of DNA. Crick redirected his scientific attention to consciousness in the latter stages of his career before his death.

 

[zoobyshoe]

I do think it's important to maintain some level of logical rigor when talking about somewhat complex subjects like this, though.

Well, I posted quite a bit, and if that was the only transgression you discovered to be worth highlighting, then there's hope.

btw, surely you know Francis Crick? Of Watson and Crick fame, discoverers of the structure of DNA. Crick redirected his scientific attention to consciousness in the latter stages of his career before his death.

I'm sure I've encountered the names before in connection with the DNA discovery, but I guess there was never any reason for it to stick in my memory. I know precious little about DNA.

 

[El Hombre Invisible]

I was reading the first link from hypnagogue, and found this interesting:

"Then these neurons are monitored in the binocular rivalry situation, to see how well they correlate with what the monkey seems to be seeing. It turns out that cells in primary visual cortex (V1) don't correlate well: when the monkey is stimulated with horizontal and vertical gratings but "sees" horizontal, a large number of "vertical" cells in V1 fire, as well as "horizontal" cells. At this point, most cells seem to correlate with retinal stimulus, not with visual percept."

Your brain knows more than you do, huh?

 

[hypnagogue]

Your brain knows more than you do, huh?

There is tons of information in the brain that is not represented in consciousness at any given time. Computationally speaking, consciousness actually has quite limited capacity with respect to the brain as a whole. We run into these limitations all the time: We can only hold a paltry 6 or 7 units of information in working memory at a time, it's impossible for us to effectively attend to two sensory modalities (e.g., seeing and hearing) at once, etc.

Consciousness's functional utility isn't so much what it knows as much as it is 'who' it knows and how it contacts them. Consciousness has widespread access to a huge number of specialized neural subsystems, each of which is very good at performing highly specific tasks. Those subsystems help shape the things we actually are conscious of-- for instance, as you read this sentence, quite complex syntactic and semantic operations on the words are being performed in your brain. You are not aware of all this low-level activity, however. What is ultimately sent to your conscious awareness is a high-level understanding of the sentence that appears to 'come' to you quite automatically and effortlessly. Once a piece of information reaches conscious awareness, it is automatically 'broadcast' widely across the brain to numerous subconscious subsystems, which can then use that information to guide further perception and behavior, etc. So, functionally speaking, consciousness acts as a sort of integrator and disseminator of information in the brain, transmitting important global messages to specialized, local subsystems that otherwise function pretty 'blindly' and independently.

 

[hypnagogue]

BTW, Crick's last paper before his death, http://www.pubs.royalsoc.ac.uk/finalcrickpaper.shtml, was recently published. The claustrum is a thin sheet of neural tissue lying beneath the cortex on either hemisphere, receiving input from and projecting to most areas of cortex. In the paper, Crick and Koch speculate that the claustrum might play a crucial role in binding and coordinating various sensory percepts within and across most sensory and motor modalities, i.e. it might be the 'conductor' that organizes all the disparate information in the various regions of cortex into one coherent and synchronized whole in consciousness. As of yet this remains speculation, since the claustrum is situated in such a way that it is extremely rare that it becomes damaged while other brain regions remain intact, and it is particularly difficult to stimulate it using invasive measures, etc.

 

[zoobyshoe]

zoobyshoe, I enjoyed your comments. Many thanks.

You're very welcome.

Here is a link to an essay that contains the Ramachandran story in which I first heard about these patients:
Address:http://consc.net/misc/wired.html

You have to scroll way, way down to the section entitled One Hand Clapping.

Ramachandran's stories about these patients are interesting, but you should be able to see why I find his psychological explanation of the problem unconvincing.

Neurologist Berti in your article is much more to my liking in that she questions the validity of ascribing this exceptionally elaborate phenomenon to a cause as flimsy as denial: refusal to face the fact you have a problem.

I'm interpreting this as if the conscious portions of the brain are working properly but receiving improper inputs or are unable to properly connect to the body.

I think this is right. More: in addition to being "out of touch" with the paralyzed half, consciousness is receiving false information from within the brain due to the various mechanisms mentioned by me, and the neurologist in the article you posted, such that it feels like the planning and execution of movements are being carried out as usual.

Berti, the doctor in your article, doesn't go as far as I did to the next step, which was to say that, completely convinced by the sensations of movement, the brain "heals" any gap there may be between that sensation and the obvious sight of a paralyzed arm or leg, by hallucinating all the proper visuals to accompany the feeling. These people, by their own testimony, "see" their arms moving, and their hands clapping. I don't think they're lying, and I think they mean it literally.

I don't know the exact mechanism by which people have visual hallucinations whose content is directed by their own will and desires, but I can speculate it is accomplished by doing something similar to what the brain does during dreaming. In addition, I think these people can fall into this easily because the stroke damage throws everything somewhat off.

Although the portions of the brain responsible for performing those functions are not working properly, the lack of those functional areas does not directly impact the ability of the brain to be conscious or aware.

In general, yes. My view on this, though, is that everything you subtract diminishes consciousness: it has less imput.

I'm sure you'd enjoy The Man Who Mistook His Wife for a Hat and An Anthropologist on Mars by Oliver Sacks. Learning what the brain does can be done in negativa, by learning what happens when parts of it go wrong. Sacks is a good writer, comes off as a warm person, and the stories are fascinating.

 

[hypnagogue]

Zantra: It sounds like that hemispherectomy must not touch certain common areas of the brain such as the thalamus which is deep in the center somewhere above the brain stem.

The thalamus is actually composed of two symmetrical parts on either side of the brain, and the two sides of the thalamus seem to perform much the same functions. For instance, we've already talked about how damage to the intralaminar nuclei in the thalamus leads to coma. However, for coma to occur, both intralaminar nuclei need to be damaged. If only one is damaged, one can still maintain consciousness. If the original hemispherectomy procedures did indeed remove an entire half of the brain, then half of the thalamus was also removed. However, the remaining half of the thalamus would have been enough to maintain consciousness. From the description Zantra posted, it seems like modern hemispherectomies do not get deep enough to affect the thalamus.

http://ahsmail.uwaterloo.ca/kin356/ltm/thalamus_hypothalamus.html is a pictorial representation of a thalamus highlighting some of its anatomical features, and again you can see its symmetry.

 

[zoobyshoe]

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.

 

[Q_Goest]

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?

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.)

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.

Note 2, it is understood that the thalamus may not contain the only NCC's, so the above can be rewritten by replacing "thalamus" with "NCC's".

 

[Q_Goest]

A general question

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 seem to remember reading somewhere that there are neurons unique to the thalamus, with thalamus sounding names, so one must conclude there is a uniqueness within them which does not corrolate to their dimensions or other outward appearances.

Perhaps I'm only offering "easy" questions as Chalmers would say, but I have to believe these questions have already been answered.

 

[Q_Goest]

zoobyshoe

Thanks once more for, this time for the link. Andrew Brown writes with a brilliant flair one can't help but notice. There's so much to read on this subject and so little time, but moments of focus such as this one are worth their weight.

 

[zoobyshoe]

I found this interview to be thought provoking:

NOVA Online | Secrets of the Mind | The Electric Brain
Address:http://www.pbs.org/wgbh/nova/mind/electric.html

 

[zoobyshoe]

Thanks once more for, this time for the link. Andrew Brown writes with a brilliant flair one can't help but notice. There's so much to read on this subject and so little time, but moments of focus such as this one are worth their weight.

Andrew Brown is...the author of that article? I didn't sample much of his "flair". I just googled "Ramachandran" and when I got there, typed his name into my find on page button. So much to read, so little time.

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. This seems to belie his whole proposition that their "denial" is psychological confabulation.

 

[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.