Hot can be cold, and cold can be hot What ?

[rhody]

Hot can be cold, and cold can be hot... What ?

Has anyone ever experienced http://www.wired.com/wiredscience/2007/10/the-bizarre-eff/" , "Ciguatoxin produces toxic effects by activation of voltage-dependent sodium channels, resulting in hyperexcitability, decreased conduction, and prolonged refractoriness. Effects are most pronounced on neuronal, cardiac, and GI tissues."

From the same article: "Paradoxical temperature reversal (eg, cold objects feel hot and hot objects feel cold) (This is a classic reported finding; however, at least one study suggests that this perception is likely the result of the exaggerated and intense nerve depolarization and that gross temperature perception remains intact)."

Can someone who is a chemist or neurologist explain how and why "exaggerated nerve depolarization" causes the brain into being fooled that cold is hot and hot is cold ? Is this effect the agreed cause, or are scientists simply groping for an answer ?

And finally, see chart below, why do these chemical compounds, http://en.wikipedia.org/wiki/Capsaicin" among them, ((CH3)2CHCH=CH(CH2)4CONHCH2C6H3-4-(OH)-3-(OCH3)) is the active component of chili peppers) make the human brain perceive themselves to be not hot in a physical sense, but hot to the taste ?

The same questions apply, how do these chemicals stimulate or fool our brains into perceiving the sensation of "hotness" applies here.

Rhody...

 

[zoobyshoe]

Has anyone ever experienced http://www.wired.com/wiredscience/2007/10/the-bizarre-eff/" , "Ciguatoxin produces toxic effects by activation of voltage-dependent sodium channels, resulting in hyperexcitability, decreased conduction, and prolonged refractoriness. Effects are most pronounced on neuronal, cardiac, and GI tissues."

From the same article: "Paradoxical temperature reversal (eg, cold objects feel hot and hot objects feel cold) (This is a classic reported finding; however, at least one study suggests that this perception is likely the result of the exaggerated and intense nerve depolarization and that gross temperature perception remains intact)."

Can someone who is a chemist or neurologist explain how and why "exaggerated nerve depolarization" causes the brain into being fooled that cold is hot and hot is cold ? Is this effect the agreed cause, or are scientists simply groping for an answer ?

I'm not a chemist or neurologist, and I have no idea how much agreement or groping is going on, but to the best of my knowledge no one has ever explained how any specific qualia results from the action of neurons. It's a question tied up with how the action of neurons leads to consciousness itself.

Regardless, things might be clarified a little. A quick google on hot and cold processing in the brain turned this paper up:

We used functional magnetic resonance imaging (fMRI) to determine whether similar brain regions activate during noxious hot and cold stimulation. Six male subjects underwent whole brain fMRI during phasic delivery of noxious hot (46 degrees C) and noxious cold (5 degrees C) stimulation to the dorsum of the left hand. Mid-brain regions activated included thalamus, basal ganglia and insula. Cortical areas activated included cingulate, somatosensory, premotor and motor cortices, as well as prefrontal and inferior parietal cortex. Most regions activated bilaterally but with stronger activation contralateral to the stimulus. Noxious cold stimulation produced significantly increased volumes of activation compared to noxious heat in prefrontal areas only. Our results suggest a similar network of regions activate common to the perception of pain produced by either noxious hot or cold stimulation.

http://www.ncbi.nlm.nih.gov/pubmed/10876085

The abstract is saying is that the pain specific to "noxious" hot and cold are processed by "similar" regions. The reason I mention it is that it suggest the possibility of a confusion or crossover of the "similar" networks due, somehow, to the toxin.

That the toxin produces hyperexitability and prolonged refractory period must certainly have been demonstrated: it's the kind of thing they could test on animals. Exactly how this leads to the reversal of hot and cold sensations may not be known, but the one study they highlight: "This is a classic reported finding; however, at least one study suggests that this perception is likely the result of the exaggerated and intense nerve depolarization and that gross temperature perception remains intact," suggests it isn't authentically reversed, that cold and heat sensations remain intact but are overlaid by peculiar qualia that roughly present as the pain of the opposite "noxious" temperature. In other words, it's actually a matter of the patients not being rigorously analytical and articulate about the strange sensation caused by the "exaggerated and intense nerve depolarization". The sentence seems to assert they actually can still tell hot from cold: "gross temperature perception remains intact".

The other symptoms listed include:

# Lingual and circumoral paresthesias: a sensation of pricking, tingling, or creeping on the skin that has no objective cause

# Painful paresthesias of the extremities

# Arthralgias: pain in one or more joints

# Myalgias: pain in one or more muscles

#Abdominal pain

so it's a toxin given to producing phantom pains, and these are, at least, correlated with the "activation of voltage-dependent sodium channels, resulting in hyperexcitability, decreased conduction, and prolonged refractoriness."

 

[physics girl phd]

http://www.fda.gov/Food/FoodSafety/FoodborneIllness/FoodborneIllnessFoodbornePathogensNaturalToxins/BadBugBook/ucm069972.htm" the chemical structure of the toxin, just in case anyone's interested.

 

[rhody]

And finally, see chart below, why do these chemical compounds, http://en.wikipedia.org/wiki/Capsaicin" among them, ((CH3)2CHCH=CH(CH2)4CONHCH2C6H3-4-(OH)-3-(OCH3)) is the active component of chili peppers) make the human brain perceive themselves to be not hot in a physical sense, but hot to the taste ?
The same questions apply, how do these chemicals stimulate or fool our brains into perceiving the sensation of "hotness" applies here.

Rhody...

result of the exaggerated and intense nerve depolarization and that gross temperature perception remains intact

and

so it's a toxin given to producing phantom pains, and these are, at least, correlated with the "activation of voltage-dependent sodium channels, resulting in hyperexcitability, decreased conduction, and prolonged refractoriness."

Thanks for the reply. This is a start, but the response given is suggestive at best...
The link I provided also said that the confused sensation(s) last days to weeks at best as well, suggesting that the toxin once removed or cleansed by the body returns to normal sensation of hot/cold, etc...

I would like to know what you think about my second question regarding capsaicin, listed above... this time not physical hotness, but hot in taste only...

BTW. I read a book awhile ago: http://www.jpans.com/ebook/phantoms-in-the-brain/", by Ramachandran, and Blakeslee on phantom pain resulting from people who lose limbs. I will dig it out to see what it has to say about fooling the brain into thinking there is pain when in fact no limb exists. I vaguely remember a cool experiment that Dr Ramachandran did that helped people with phantom pain learn to control and alleviate it.

This explanation of the perception and control of phantom pain may help lead to a better understanding of the hot/cold issue, and hot in taste only issue. I will reread that section and try to summarize the experiment and why the patient was relieved of the pain according to Dr. Ramachandran.


Rhody...

 

[zoobyshoe]

Thanks for the reply. This is a start, but the response given is suggestive at best...

The only comprehensive response would involve an explanation of how qualia are created in the first place, a thing which no one has figured out, and may never. We know a lot about where conscious experiences are created, but little about how they are created.

The link I provided also said that the confused sensation(s) last days to weeks at best as well, suggesting that the toxin once removed or cleansed by the body returns to normal sensation of hot/cold, etc...

Yes, it seems to be temporary.

I would like to know what you think about my second question regarding capsaicin, listed above... this time not physical hotness, but hot in taste only...

I have never looked into the action of taste buds, but I'm sure it's been exhaustively researched and all the actions of various chemicals on the receptors finely parsed. Here again, it's a matter of qualia. Asking why capsaicin is experienced as "hot" is the same as asking why blue is experienced as blue.

BTW. I read a book awhile ago: http://www.jpans.com/ebook/phantoms-in-the-brain/", by Ramachandran, and Blakeslee on phantom pain resulting from people who lose limbs. I will dig it out to see what it has to say about fooling the brain into thinking there is pain when in fact no limb exists. I vaguely remember a cool experiment that Dr Ramachandran did that helped people with phantom pain learn to control and alleviate it.

This explanation of the perception and control of phantom pain may help lead to a better understanding of the hot/cold issue, and hot in taste only issue. I will reread that section and try to summarize the experiment and why the patient was relieved of the pain according to Dr. Ramachandran.

I'm familiar with that book, and while he made a great deal of headway in explaining phantom sensations of touch and proprioception, the explanation of phantom pain was more elusive. That's really the one they want to solve since it's the most troublesome.

Since people suffering from this fish borne toxin aren't amputees it would seem the exact mechanism is different, but maybe not. Perhaps the nerves of amputees are prone to the same hyperexitability and refractory problems producing the phantom pain. Phantom touch and phantom proprioception are the result of a different mechanism, though, as explained by Ramachandran.

 

[rhody]

Phantom touch and phantom proprioception are the result of a different mechanism, though, as explained by Ramachandran.

That one, "proprioception", threw me, I checked the definition. Do you mean, from http://en.wikipedia.org/wiki/Proprioception"

In humans, a distinction is made between conscious proprioception and unconscious proprioception:

* Conscious proprioception is communicated by the posterior column-medial lemniscus pathway to the cerebrum.

* Unconscious proprioception is communicated primarily via the dorsal spinocerebellar tract, to the cerebellum.
o Such an unconscious reaction is seen in the human proprioceptive reflex. This remarkable proprioceptive reflex (Law of Righting) will cock the head back to level the eyes against the horizon. This is seen even in infants as soon as they gain control of their neck muscles. This comes from the cerebellum, the part of the brain affecting balance.

I am checking the book for the explanation of relief of phantom pain now, but wanted to post this first.

Found it. I will try to summarize briefly

From pages, 46-49. Dr Ramachandran constructs a virtual reality box with a vertical mirror on the right side of the box. When one hand is inserted, the person sees the real hand and the vertical reflection of that hand in the other side (phantom hand). The brain receives visual feedback that the hand is moving in correct response to commands.

His patient, Phillip lost left arm in a motorcycle accident ten years ago, and has suffered phantom pain in the phantom elbow. wrist, and fingers. Phillip claimed that he could never move his phantom arm. The Dr wondered if it was "learned paralysis". When Phillip placed his good right hand in the box and observed his left arm ,he freaked. He could suddenly move the elbow, wrist and fingers again. However, as soon as he closed his eyes, it became frozen again.

The Dr suspected that learned paralysis could be undone with enough practice and time with the box. He allowed Phillip to take it home and practice, which he did for three weeks.

Phillip called the Dr after three weeks, and I will quote Phillip from the book, page 49, "Doctor, it's gone, What is gone ?", replied the Dr, "My phantom is gone, What are you talking about ? You know, my phantom arm, which I had for ten years. It doesn't exist anymore. All I have is my phantom fingers and palm dangling from my shoulder."

Phillip went on to explain that the intermittent pain in his elbow was gone. He explained that since he still had his fingers dangling from his shoulder that they still hurt. According to Dr Ramachandran, Phillip's right parietal lobe was presented with conflicting signals, visual feedback telling him his arm is moving again while his muscles telling him his arm is not there, the mind resorted to a form of denial. The only way his overstimulated brain could deal with it was to say, to hell with it, there is NO arm.

I then read the section on qualia pages 229-230 to try to put the definition of qualia perspective, where the Dr describes someone who is color blind, can describe the wave lengths that make the color red, but because the person lacks the cone receptors in the eye, they can never experience what the person who has cones sees as red. The experience is only subject to the viewer, in this case one with cones in his eyes and one without. So that leaves us back where we started, your sentence from a previous post:

We know a lot about where conscious experiences are created, but little about how they are created.

The only new information here is that somehow Phillip's brain rewired itself over a three week period when presented with new, but conflicting stimuli of having part of his phantom arm back. Experiments to document this would be pretty hard I imagine, you would have to be lucky enough to use some real time brain imaging of a healthy person, as they moved a good limb, and then due to unfortunate circumstances after an accident an amputation subject that same person to the experiment described above, probably every few days to see if the changes could be seen evolving in the brain that resulted in Phillip's final perception of his phantom arm. The chances of that ever happening are slim to none I would guess. But I may be wrong. Even then you would only see the "what" of the changes in brain activity, never the why...

Rhody...

P.S. My real fingers hurt (pun intended) from typing this... lol

 

[zoobyshoe]

That one, "proprioception", threw me, I checked the definition. Do you mean, from http://en.wikipedia.org/wiki/Proprioception"

In humans, a distinction is made between conscious proprioception and unconscious proprioception:

* Conscious proprioception is communicated by the posterior column-medial lemniscus pathway to the cerebrum.

* Unconscious proprioception is communicated primarily via the dorsal spinocerebellar tract, to the cerebellum.
o Such an unconscious reaction is seen in the human proprioceptive reflex. This remarkable proprioceptive reflex (Law of Righting) will cock the head back to level the eyes against the horizon. This is seen even in infants as soon as they gain control of their neck muscles. This comes from the cerebellum, the part of the brain affecting balance.

I am checking the book for the explanation of relief of phantom pain now, but wanted to post this first.

Rhody...

Yeah, that Wiki article is what I meant. (I had never seen it divided into conscious and unconscious before, though.) Proprioception is the sense of where your body parts are located relative to each other. It's a dedicated system distinct from touch with it's own specialized receptors in the body and processing neurons spread throughout the parietal lobes.

You can easily demonstrate you have such a sense by closing your eyes and putting your arms in various positions. Without having to look, you automatically know what position your arms are in.

Most people with phantom limbs have elaborate proprioceptive sensations in those phantoms: they can tell you instantly what position the phantom is in. They can move the phantom, (and some even feel they can touch things with the phantom and feel the touch).

Some have the strange experience of "telescoping" phantoms. At rest, someone who has lost their arm might "feel" their hand dangling directly off the shoulder. When they want to do something with the phantom they can "make" it telescope out to full length. That's about the strangest most interesting thing I've read about phantom limbs. This is clearly a proprioceptive and kinaesthetic illusion combined.

In The Man Who Tasted Shapes, author Cytowic describes, among other people, one case of a synaesthete whose sense of hearing was linked up with his sense of proprioception. The sound of certain words caused him to feel the strong urge to put his body in specific and unusual positions in response to those words. That might sound like some kind of Tourettes, but he was tested over years in such a way that the synaesthesia diagnosis was confirmed.

Come to think of it, the best area of reading for you regarding your question might be the in the field of synaesthesia, the peculiar condition some people are born with where a stimulus to one sense causes a simultaneous reaction in a second sense. The most common pairing is sound and vision.

 

[rhody]

zoobyshoe,

Please read my last post again. I edited it and you may have missed it because you were posting before I finished.

Rhody...

 

[zoobyshoe]

zoobyshoe,

Please read my last post again. I edited it and you may have missed it because you were posting before I finished.

Rhody...

Yes, that whole story underscores the mystery of phantom pain.

I don't remember if Ramachandran or Sacks points this out but the strange fact is that the experience of phantom pain is dependent on the degree of feeling in the limb at the time of removal. When a limb is surgically removed they can completely avoid phantom pain by numbing the limb with local anaesthetic (not general, local) before the surgery. People who lose limbs suddenly in accidents, or who have a limb removed under general anesthetic alone, will feel phantom pains. There is an important element of "memory" of the injury in it, somehow, as if, in the absence of subsequent "everything's now OK" signals from the limb, the brain's pain centers keep interpreting all signals from the remainder of the limb as repetitions of the last verifiable transmission, which was an urgent SOS, or in the case of removal under local anesthetic, no signal at all.

Is the mirror box a form of hypnotic anesthetic? What are the neural correlates of hypnosis? Could we see someone's brain function changing under hypnosis with a pet scam or fmri? There is really a lot more for Ramachandran to explore, and I wish he would. There seems to be few others interested. That whole book arose from his curiosity about reports from patients that other neurologists outright dismiss and ignore.

There was another couple studies posted and discussed here by different researchers which demonstrated that proprioception is normally supported by vision and touch, and the brain expects the three to all concur about body position. When one is made to contradict the other two, the brain tends to believe vision over the others. I can dig them up if you're interested. They are variations of the mirror box applied to normal people to make them see themselves or parts of themselves in positions they are not actually in.

The question I would have about the parethesias and myalgias of the fish toxin is whether they result from the signals from the body to the brain being screwed up, or from the way the brain processes the signals being screwed up, or both.

 

[rhody]

Is the mirror box a form of hypnotic anesthetic? What are the neural correlates of hypnosis? Could we see someone's brain function changing under hypnosis with a pet scam or fmri? There is really a lot more for Ramachandran to explore, and I wish he would. There seems to be few others interested. That whole book arose from his curiosity about reports from patients that other neurologists outright dismiss and ignore.

The question I would have about the parethesias and myalgias of the fish toxin is whether they result from the signals from the body to the brain being screwed up, or from the way the brain processes the signals being screwed up, or both.

I agree. It seems that one mystery leads to another, derived from different sense(s) and modalities. You raise good questions and introduce more subjects than we started with, not a bad thing. I will do some research on synaesthesia in the meantime as you suggest. (Any links would be appreciated, hint, hint)

Would it be fair to say that there are areas of the brain devoted to processing overlapping (and at times confused) diverse sensory input, real, imagined, and as we have seen from real and phantom body parts ?

It would be cool if there were a common thread or threads to all of this. And if it, or they exist, once discovered and verified scientifically, would lead us to a much deeper understanding of all of the the strange "qualia" as you put it. For now, having a deeper understanding of the "what" may be the best we can do. Maybe the "why", the hard one, is simply beyond all human understanding...

Rhody...

 

[fuzzyfelt]

I know some people who have had this. I think distinguishing black, white and grey can be used as a diagnostic test, which might be of interest.

 

[zoobyshoe]

I agree. It seems that one mystery leads to another, derived from different sense(s) and modalities. You raise good questions and introduce more subjects than we started with, not a bad thing. I will do some research on synaesthesia in the meantime as you suggest. (Any links would be appreciated, hint, hint)

Richard Cytowic is to syaesthesia as Ramachandran is to phantom limbs, in the sense he's done more listening to people who have it than anyone else I've read about. His book The Man Who Tasted Shapes is a must read intro to the phenomenon. (Try Amazon or Ebay for an inexpensive used copy. Also check your public library.) After reading that you'll be better prepared for some denser papers he has online. Oliver Sacks and Ramachandran also describe cases here and there, but Cytowic is pretty exclusively dedicated to the phenomenon.

Would it be fair to say that there are areas of the brain devoted to processing overlapping (and at times confused) diverse sensory input, real, imagined, and as we have seen from real and phantom body parts ?

This is hard to answer. The more you learn, the more you might be inclined to abandon the question. Any part of the brain can communicate with any other part of the brain, but some connections are more circuitous and less informative than others. Just about all experience is always being compared to memory, but memory can be parsed into different forms that seem to be processed at different locations. The occipital lobes are considered to be the visual cortex, yet important aspects of vision are processed in the temporal lobes such that most elaborate visual hallucinations are believed to be of temporal lobe origin. The processing of overlapping information takes place all over the place and differential comparisons of one form or another are most likely ubiquitous, depending on what's being differentiated from what and at what level. A lot of brain scan studies are still aimed at mapping out what parts of the brain kick in when x stimulus is being processed, like the hot and cold study I linked to above. On the other hand I might assert that the frontal lobes, where what we call "thinking" is said to take place, are most responsible for sorting out apparent contradictions.

It would be cool if there were a common thread or threads to all of this. And if it, or they exist, once discovered and verified scientifically, would lead us to a much deeper understanding of all of the the strange "qualia" as you put it. For now, having a deeper understanding of the "what" may be the best we can do. Maybe the "why", the hard one, is simply beyond all human understanding...

The issue of "qualia" is this: why is it that we experience a toothache, for example, in precisely the form we do? Why shouldn't a toothache feel like, say, burning, and burning like a toothache? Why is red red and not red? The stimulus is real (electro-magnetic radiation), but the exact experience it causes is arbitrary and might have evolved into anyone of another arbitrary experiences. People with synesthesia learn to interpret and rely on their altered responses, coordinating them with all other sensory experiences, to arrive at useful information about their environment, which pretty much demonstrates that the experiences we actually have aren't written in stone as the only possible, or the only "real" experiences necessary to interact in a practical way with the environment around us. It's been posited that bats experience the information they receive from their ultrasonic echos as full blown visual pictures. There's no reason sound couldn't be processed into visual experiences, synesthetes do it, so this is not outlandish.

Actually, I just mushed two separate issues together. The real question is not why one qualia was selected over another, but how the actions of neurons lead to any qualia at all.

What makes qualia what it is, is intimately tied up with the question of how the action of neurons leads to consciousness. Every one wants to know, but personally I'm not eager for that question to be answered because it's only going to lead to people making, or trying to make, artificial consciousness in the lab, and that could be a nightmare.

 

[rhody]

Any part of the brain can communicate with any other part of the brain, but some connections are more circuitous and less informative than others.

This is a bit off topic but everything I have read says http://en.wikipedia.org/wiki/Split-brain" "that severing the entire corpus callosum blocks the interhemispheric transfer of perceptual, sensory, motor, gnostic and other forms of information in a dramatic way. This allowed Gazzaniga and Sperry to gain insights into hemispheric differences as well as the mechanisms through which the two hemispheres interact." To me, a layman, that says there are parts of the brain, in this case without a fully connected/functional left and right corpus callosum that full integration and communication of specialized areas of the brain would not be possible, no ?

What makes qualia what it is, is intimately tied up with the question of how the action of neurons leads to consciousness. Every one wants to know, but personally I'm not eager for that question to be answered because it's only going to lead to people making, or trying to make, artificial consciousness in the lab, and that could be a nightmare.

Again, a bit off topic, but I have read a few articles and did a quick search to prove my point, scientists are in the process of working on "artificial consciousness". In your words, "a nightmare" is well underway. http://discovermagazine.com/2009/feb/16-what-makes-you-uniquely-you/article_view?b_start:int=1&-C=" The google search returned 538,000 hits so here is great interest in this field.

As to your last post the other day I haven't had time to find or get the book on synaesthesia, "The Man who Tasted Shapes", which I will do in the near future, and see if there is any new insight to be gained from it. I will report back, but it will take some time.

I know the world of quantum mechanics lies beneath the microscopic world being discussed here, and like it or not, unless physics has some radical new insight or breakthrough to replace quantum theory in the next decade or two, we will be left to try to formulate new theories for qualia based on QM, where probability and uncertainty rule. This is where true mysteries lie and what drives me to want to study it. Either from the top down or from the bottom up, I will take what I can get if it leads to a more complete understanding.

Back in 2005-2006 I was fortunate enough to freely download a paper co-authored by Roger Penrose and Stuart Hammeroff: A new theory of the origin of cancer: Quantum coherent entanglement, centrioles, mitosis and differentiation, which has since been put under pay for access only. I have a copy that I have red-lined if you are interested.

Note: I edited this post and uploaded the Penrose/Hammeroff paper in 2 parts, the red outlined text is of interest, the blue text is where I added a comment or a question.

In the paper, the authors explore the role that quantum mechanics may be involved within the brain, describing the details of the "what" and "how". What hooked me into paying attention to this paper in the first place was reading Penrose's, The http://www.10xdownloads.com/checkin...ose, Roger - The Emperor's New Mind.pdf&cr=1" in 1989, where he argues that known laws of physics are inadequate to explain the phenomenon of human consciousness. Penrose hints at the characteristics this new physics may have and specifies the requirements for a bridge between classical and quantum mechanics (what he terms correct quantum gravity, CQG).

I will end here for now, except to say if it were not for reading Penrose's book back in 1989 I would not be writing this post in 2010.

Rhody...

 

[Eric McClean]

Awesome information , i have never come across with this fact ever.
Thanks for sharing.

 

[rhody]

Awesome information , i have never come across with this fact ever.
Thanks for sharing.

Do you mean this ?

P.S. My real fingers hurt (pun intended) from typing this... lol.

Seriously Eric, what "fact" are you referring to ?

Rhody...

 

[rhody]

It has been awhile since I reported anything n this thread, however, sometimes you find little gems, "hiding in plain sight" in this case on our forum,
under the Sci Am category: http://www.scientificamerican.com/article.cfm?id=playing-the-body-electric".

A summary from the article is provided, followed by main details:

A judicious mix of recombinant DNA technology, protein and viral design, genomics, optical fibers, lasers and micro-instrumentation will enable scientists to explore strange new theories that close the gap between the objective brain and the subjective mind, to boldly go where no one has gone before.

The article states there are over 1000 subtypes of nerve cells and supporting actors, the http://en.wikipedia.org/wiki/Glial_cell" .

The study of the brain has been advanced with a combination of molecular biology with optical stimulation, named: http://en.wikipedia.org/wiki/Optogenetics" It is based on the discoveries of three German biophysicists: Peter Hegemann, Ernst Bamberg and Georg Nagel working on photoreceptors in ancient bacteria. The photoreceptors convert convert incoming light in the blue part of the spectrum into an excitatory, positive electrical signal. They found the gene for this protein, called channelrhodopsin-2 or (ChR2).

From the article:

The group took the ChR2 gene, inserted it into a small virus, and infected neurons with this virus. Many of the neurons took up the foreign instructions, synthesized ChR2 protein and inserted the photoreceptors in their membrane. In the dark, the receptors quietly sit there, with no discernible effect on their host cells. But illumination of the network with a brief flash (10 milliseconds) of blue light causes each of these bacterial photoreceptors to jolt their host cell a bit. Collectively, they reliably and repeatedly produce a spike in the membrane voltage. Spikes are the universal all-or-none pulses used by all but the tiniest nervous systems to communicate information among neurons. Each time the light is turned on, the cells spike reliably, exactly once. Thus, an entire population of neurons can be manipulated by precisely timed stabs of light.

The biophysicists added another photoreceptor to their tool kit. It derives from a different type of bacterium, one living in dry salt lakes in the Sahara Desert. Shining yellow light on it yields an inhibitory, negative signal. Through the same viral strategy, both photoreceptor types were then introduced into neurons. Once the neuron stably incorporates both types into its membrane, it can be excited by blue light and subdued by yellow. Each blue flash evokes a spike, like a note sounding when a piano key is pushed down. But a simultaneous flash of yellow light can block that spike. Consider the “musical score sheet” recorded from one such neuron as it is played with light. This ability to precisely control electrical activity in one or more neurons is unprecedented.

Here comes the cool part,

Without going into the nitty gritty details they introduce a small amount of virus that carries the ChR2 gene into a specific structure in the brain, in this case into the lateral hypothalamus of a mouse's brain, into an area that produces a hormone that promotes wakefulness. Using a light from a pulsed fiber optic probe to stimulate the area with the ChR2 cells, they were able to prove that indeed these cells when stimulated in a sleeping mouse would produce waves of spikes in the hormone receptors, and within a minute would wake the sleeping mouse reliably.

Pretty amazing if you ask me.

This same technique has been extended to uncover specific brain circuits involved in a variety of normal and pathological behaviors: depression, behavioral conditioning, Parkinson’s disease and cortical oscillations critical for attention, among others.

To summarize, from the article:

The import of optogenetics for consciousness is that it allows testing of a specific hypothesis about the neural basis of consciousness. For instance, to what extent is feedback from higher cortical regions to lower regions essential? Find out by training an animal in a task that depends on conscious sensation, then inactivate those circuit elements with light and observe the animal’s behavior.

For the first time we have have a Toolkit that will allow us to explore selected brain areas, then observe via stimulation (fiber optic light pulses) predicted responses and to test for unconventional ones as well.

Rhody...

P.S. I have started the book, "The Man Who Tasted Shapes" by Cytowic, and hopefully soon I will have something to present/discuss here.