<p>This is an interesting idea, but I do not think it's correct. One piece of information that goes against the idea is this: auditory information is encoded by both frequency and amplitude modulation of neural spiking. The idea of spiking rate directly correlating with frequency is at odds with the idea of spiking rate containing this sort of "meta" information about the source of the activity.</p>

<p>We know quite a lot about how sensory information is represented in the nervous system. The simple fact of myelinated axons that don't interfere with each other already accounts for the problem you've proposed a solution for. </p>

<blockquote>
  <p>if all 3 types of cone cells generated identical responses for a given rate-of-incidence... then there would be no way for upstream neurons to tell what type of cone cell a spike sequence came from</p>
</blockquote>

<p>Here I believe is where you've made an error. The transmission of activity from the sensory neuron itself to an upstream neuron inherently conveys information about the sensation. The firing of the sensory neuron is a translation of the external phenomena to an internal neural code. No extra information is needed to represent the source of the activity.</p>

<p><strong>References</strong></p>

<p>Li Liang, L., Lu, T., &amp; Wang, X. (2002) <a href="http://jn.physiology.org/content/87/5/2237.full.pdf+html" rel="nofollow">Neural Representations of Sinusoidal Amplitude and Frequency Modulations in the Primary Auditory Cortex of Awake Primates</a>. <em>J. Neurophysiol</em> 87:2237-2261.</p>

CC BY-SA 3.0
2012-07-25T08:49:19.697Z
This is surely more effective than the 5 page tome on the visual system I was thinking about writing! Nice work.
Chuck Sherrington
CC BY-SA 3.0
2012-07-26T07:39:24.227Z
Your description of the auditory system seems to be at odds with what I've read elsewhere, [von Bekesy's Place Theory](http://en.wikipedia.org/wiki/Georg_von_B%C3%A9k%C3%A9sy), which essentially says that the cochlea does a **Fourier transform** of the input pressure wave recorded by the eardrum. Also, I feel you have missed the problem I'm describing, here's another attempt: If red/blue/green are all converted to the same neural code, a rate coded spike stream, how do upper regions know which is which?
bfrs
CC BY-SA 3.0
2012-07-26T08:02:17.583Z
@bfrs Auditory physiology has advanced significantly since Bekesy. The paper I linked shows this, and you can find many more on the same subject. I do not believe I have misunderstood you. You're not considering that the individuality of neurons is itself a type of encoding. The upper regions know which is which because different retinal ganglion cells (simplification here) respond to different colors. When a green/red ganglion cell fires, it is informing the upper regions that there is green/red within that place on the retina. No extra information needs to be encoded in the firing rate.
Preece
CC BY-SA 3.0
2012-07-26T08:17:31.463Z
@Preece Thanks for responding. Ok, here's where I keep getting confused: What if right after the green/red ganglion's firing, a blue/yellow ganglion right next to it fires...how does the upper region know its not another (or the previous) green/red one firing a second time?
bfrs
CC BY-SA 3.0
2012-07-26T08:19:14.613Z
@bfrs Because each ganglion cell has it's own axonal projection to the LGN. The LGN is more or less a topographical map of ganglion cells, so the information is preserved.
Preece
CC BY-SA 3.0
2012-07-26T08:34:35.513Z
@Preece I guess I have some reading to do to understand how the LGN creates its topographical map. Any suggestions for a good source of reading material?
bfrs
CC BY-SA 3.0
2012-07-26T08:56:58.583Z
@Preece I hope you have not missed the new section I added to the question: **Why (I think) message type must be encoded in the message itself**
bfrs
CC BY-SA 3.0
2012-07-26T09:36:01.330Z
@bfrs Start thinking in terms of activity. That is what counts. The neurons can be considered conduits for this activity. Activity generated by some external happening travels into the nervous system, and that activity inherently represents what caused it. That is the foundation of the functioning of the nervous system, and it can be a little difficult to digest. Here is one more example to clarify: how does the nervous system differentiate between a touch on the toe and on the finger? Because the sensory neurons in the toe *inherently* represent activity there. No need to code the location.
Preece
CC BY-SA 3.0
2012-07-26T22:33:04.807Z
let us [continue this discussion in chat](http://chat.stackexchange.com/rooms/4263/discussion-between-bfrs-and-preece)
bfrs
CC BY-SA 3.0
2012-07-25T08:42:59.013Z
2012-08-14T23:49:59.077Z
2012-08-14T23:49:59.077Z
Preece
<p>After an <em>eye opening</em> experience rereading Hubel's book, <a href="http://hubel.med.harvard.edu/book/bcontex.htm" rel="nofollow">Eye, Brain &amp; Vision</a> and a bunch of papers, I found that the answer to my question is a superficial <em>yes</em> and a strong <strong>no</strong>. </p>

<p>It is unsurprising that <a href="http://www.ploscompbiol.org/article/info%3adoi/10.1371/journal.pcbi.1000433" rel="nofollow">neuroscientists have investigated</a> if there are analog characteristics to neural spike streams: </p>

<blockquote>
  <p>Neurons communicate with each other using stereotyped electric pulses,
  called spikes. It is believed that neurons  convey no information
  other than the frequency of the transmitted spikes, called the firing
  rate. However, it is possible that neurons may communicate some
  information through the finer temporal patterns of the spikes because
  biological, as well as electrical/mechanical signals generally reveal
  internal conditions of the signal generator...</p>
  
  <p>... First, we found that
  neurons exhibit stable firing patterns that can be characterized as
  “regular”, “random”, and “bursty”. Second, we observed a strong
  correlation between the type of signaling pattern exhibited by neurons
  in a given area and the function of that area.</p>
</blockquote>

<p>So, in a superficial sense the answer is yes, sensory neurons might have characteristic firing patterns. However, when it comes to transmitting generic analog signals, neurons have one big handicap: <strong><em>any analog features in the signal are lost at synaptic junctions, where the electrical signal is transformed into a chemical message.</em></strong> </p>

<p>One way to preserve at least part of the analog information, say message type encoded in a characteristic pattern, might be to have the message transmitted over <em>a sequence of neurons of the same size and type which all fire in a similar way</em>. However, in the visual system, there is no evidence for this. The retinal ganglion cells have their axons end in the LGN whose neurons are very different, and these in turn send their spikes to V1 whose neurons are again different. So, any characteristic patterns generated by the ganglions are lost in the LGN synapses. </p>

<p>The bigger question still remains: how do upper regions figure out what type of ganglion is sending the spike stream? (I'll formulate this more properly as a separate question). </p>

CC BY-SA 3.0
2012-07-26T13:29:29.417Z
to your final question. Did you spend time thinking [about my comment](http://cogsci.stackexchange.com/questions/1455/does-each-sensory-neuron-type-have-a-characteristic-spike-sequence-pattern/1476#comment2649_1455). The key part of neural-networks is their wiring pattern, I recommend reading a bit of wikipedia before follow up questions, though.
Artem Kaznatcheev
CC BY-SA 3.0
2012-07-26T22:24:20.400Z
to whoever downvoted, could you comment on what you found wrong with my answer.
bfrs
CC BY-SA 3.0
2012-07-26T22:30:42.670Z
@ArtemKaznatcheev instead of the blog post promised, I added a new section to the question. In essence what I'm trying to convey is that unlike a human designed NN or chip where the wiring is completely pre-specified, in the brain, the genetic code does not seem to do this.
bfrs
CC BY-SA 3.0
2012-07-26T22:39:50.627Z
there are plenty of NN where the wiring is not specified initially. Why don't you look up the cascade correlation algorithm or some of the questions I asked. Making significant edits to a question after it has been answered is considered poor form.
Artem Kaznatcheev
CC BY-SA 3.0
2012-07-26T23:14:35.053Z
`How do upper regions figure out what type of ganglion is sending the spike stream?` Receptive fields.  Neurons with one type of receptive field in the retina are mapped onto those with a similar receptive field in the thalamus (the notion of topography that Preece mentions) which map onto neurons with a similar receptive field in higher centers.  I reaffirm that a bout with a good textbook will open these worlds up to you.
Chuck Sherrington
CC BY-SA 3.0
2012-07-26T07:15:06.580Z
2012-07-26T22:22:40.993Z
2012-07-26T22:22:40.993Z
bfrs
<h1>Background</h1>
<p>It is known that all sensory information is input to the brain as neural spike sequences. Now, to distinguish between the spike sequences generated by retinal red/blue/green cone cells from each other, and these from the cochlear (inner ear) hair cells, and so on, some sort of encoding scheme must be used.</p>
<p>To further clarify, in the case of retinal cone cells, the rate of incident light quanta in a given energy range, is the primary information that is coded. But, if all 3 types of cone cells generated identical responses for a given rate-of-incidence, like the <a href="http://en.wikipedia.org/wiki/Charge-coupled_device#Color_cameras" rel="nofollow noreferrer">CCD pixels</a> in our digital cameras do, then there would be no way for upstream neurons to tell what type of cone cell a spike sequence came from. Instead, my guess is that, each type of cone cell encodes the rate-of-incidence in its own characteristic way, <em>similar to how different types of musical instruments sound differently, even when playing the same pitch at the same intensity, via <a href="http://en.wikipedia.org/wiki/Timbre" rel="nofollow noreferrer">timbre</a></em>.</p>
<p><img src="https://i.sstatic.net/di4o5.png" alt="enter image description here" /></p>
<p><a href="http://curtismacdonald.com/harmony-and-timbre/" rel="nofollow noreferrer">An oversimplified illustration of Timbre</a></p>
<h1>Question</h1>
<p><strong>Is there evidence that each sensory neuron type has a characteristic spike sequence pattern?</strong></p>
<h1>Why message type must be encoded in the message itself</h1>
<p>During the <a href="http://www.ncbi.nlm.nih.gov/pubmed/10888368" rel="nofollow noreferrer">development of the visual system</a>, the retina, the LGN and the visual cortex develop separately initially and sometime later, axons from the retinal ganglions grow into LGN, and optic radiations from the LGN grow and reach into the cortex. <em>As far as we can tell</em> it is not guaranteed that a specific ganglion will project its axon to a specific neuron in the LGN. All that is guaranteed by the growth process is that ganglions close together will project to LGN neurons that are also close together.</p>
<p>Given this development process, when a higher region say in the V1 receives a spike stream from a neuron somewhere lower, the question arises: how does it know that this spike stream means, red, blue or green? A simple idea that occurred to me from <a href="http://en.wikipedia.org/wiki/Information_theory" rel="nofollow noreferrer">information theory</a> is that the message type could somehow be encoded in the message itself.</p>
<h1>Motivation</h1>
<p>Evidence for characteristic spike patterns for each sensory neuron type would take us one more step towards understanding <a href="http://en.wikipedia.org/wiki/Qualia" rel="nofollow noreferrer">qualia</a>, <a href="http://en.wikipedia.org/wiki/Hard_problem_of_consciousness" rel="nofollow noreferrer">the hard problem of consciousness</a>. <em><strong>My speculation is that qualia are the neuronal analogs of timbre in musical instruments.</strong></em></p>
<p>Erwin Schrödinger thought we'd never get there. <a href="http://en.wikipedia.org/wiki/Qualia#Erwin_Schr.C3.B6dinger" rel="nofollow noreferrer">He said</a>, <em>&quot;The sensation of color cannot be accounted for by the physicist's objective picture of light [as] waves [or as quanta]. Could the physiologist account for it, if he had fuller knowledge than he has of the processes in the retina and the nervous processes set up by them in the optical nerve bundles and in the brain? I do not think so.&quot;</em></p>
<p>I guess he's right in the sense that we will never be able to fully wrap our minds around the mysterious and ineffable nature of qualia.</p>
<p>However, evidence of characteristic spike patterns would offer resolutions to qualia related thought experiments, such as <a href="http://en.wikipedia.org/wiki/Mary%27s_room" rel="nofollow noreferrer">Is there something about Mary?</a>, that philosophers seem to be <a href="http://ase.tufts.edu/cogstud/papers/RoboMaryfinal.htm" rel="nofollow noreferrer">pulling their hair out over</a>.</p>

CC BY-SA 3.0
2012-07-22T08:44:01.040Z
`if all 3 types of cone cells generated identical responses for a given rate-of-incidence ... then there would be no way for upstream neurons to tell what type of cone cell a spike sequence came from.` The previous statement is false: Neurons don't just dump all their information onto one channel, they each have an axon that runs into further regions, thus up-stream neurons have information on which cone (and thus what type of cone) is sending simply by the pattern of wiring.
Artem Kaznatcheev
CC BY-SA 3.0
2012-07-22T08:45:15.137Z
There is quite a bit known about vision, any intro textbook should tell you quite a bit (or even [Visual System](http://en.wikipedia.org/wiki/Visual_system)).  To be honest, I'm not quite sure what you're getting at with this question.
Chuck Sherrington
CC BY-SA 3.0
2012-07-22T08:46:50.223Z
I agree with @ChuckSherrington I think your motivation/background is a red-herring that leaves plenty of room for questioning your question. I would remove it and try to focus on the technical part of your query. Leave the possible connections to qualia for later. Also, to avoid the comment thread swelling like it has on previous questions, feel free to [join us in chat](http://chat.stackexchange.com/rooms/2250/the-axon-terminal).
Artem Kaznatcheev
CC BY-SA 3.0
2012-07-22T08:58:18.583Z
See the [Retinal Ganglion](http://en.wikipedia.org/wiki/Retinal_ganglion_cell) article on Wiki as well, that will tell you about some of the intermediate processing going on in the retina before the information is sent to the thalamus.  In general, this *is* a rate code, but it's more specific to whether the stimulus is on or off center in the field or the degree to which it is red or green (blue gets a bit more complicated).
Chuck Sherrington
CC BY-SA 3.0
2012-07-22T22:07:24.257Z
@ArtemKaznatcheev Regarding getting meta information simply from the pattern of wiring, this is a good point and an easy mistake to make, which a few of my friends also raised. The answer is somewhat subtle, deserving of a full blog post. I'll put a link to it as soon as I've finished it.
bfrs
CC BY-SA 3.0
2012-07-22T22:10:03.940Z
@ChuckSherrington I have read the relevant portions from David Hubel's book, [Eye, Brain & Vision](http://hubel.med.harvard.edu/book/bcontex.htm). It does contain a ton of delightful information. Hubel was among the first to record from individual neurons in V1. However, it looks like he and other neuroscientists have overlooked this aspect. Like I have said above, evidence for characteristic spike patterns would resolve a lot of questions regarding qualia. I'll give the details in a blog post.
bfrs
CC BY-SA 3.0
2012-07-22T22:12:05.747Z
@ArtemKaznatcheev This question arose out of several deep meditations on qualia over the last few days and it is at the heart of my tentative explanation of qualia. If you don't like the background, simply ignore it. I'm sure a lot of people will find it very interesting and relevant.
bfrs
CC BY-SA 3.0
2012-07-22T22:57:30.500Z
@bfrs I think what I personally am having the hardest time with is that you're glazing over about 40 years of other research that has led to insights in this area.  I am definitely familiar with Hubel, his work was seminal.  You would probably find out with further research that there may be a reason why it was "overlooked."  The fact that things like directionality, etc., have already been established to operate by rate codes derails a substantial portion of what you claim.  I think this question may be better served in a philosophical context if you're going to ignore the existing work.
Chuck Sherrington
CC BY-SA 3.0
2012-07-23T07:20:23.163Z
@ChuckSherrington The fact that a *rate code* is used does not in the slightest effect my claim. The *musical instrument* metaphor that I gave should make this clear.
bfrs
CC BY-SA 3.0
2012-07-23T07:25:39.327Z
@bfrs I'm not going to continue this discussion with you until you've read a bit more about the *actual*, *established*, scientific research in this area and you come to the table with a literature reference.  I think you've got a lot of passion about this, and that's fantastic (honest) but you need to have the basic physiological facts before you challenge the establishment with an idea.  As of right now, you're only using smoke and mirrors to do so.
Chuck Sherrington
CC BY-SA 3.0
2012-07-25T06:00:30.060Z
@ChuckSherrington Point noted. I have been rereading Hubel and realized that I missed the bulk of the details during my earlier reading. BTW, this idea does not challenge the establishment, it is only a minor embellishment on established research.
bfrs
CC BY-SA 3.0
2012-07-25T07:46:57.430Z
@bfrs Try the following approach.  Set aside the color issue for now, as that complicates things for now.  Imagine a vertebrate looking at a backdrop that has a large black horizontal line drawn on it and nothing more.  Trace the image of that horizontal line from the retina, through the retinal ganglion, up to the lateral geniculate nucleus, and into V1.  This will familiarize you with the concept of receptive fields.  As you're studying the receptive fields, note the role that rate coding plays in their relay of the information through the nuclei.
Chuck Sherrington
CC BY-SA 3.0
2012-07-25T07:49:35.193Z
con't.  See if your local library has [this book](http://www.amazon.com/Essentials-Neural-Science-Behavior-Kandel/dp/0838522459/ref=sr_1_3?ie=UTF8&qid=1343202472&sr=8-3&keywords=kandel+fundamental+of+neural) or if they can order it for you.  It has an excellent description of the visual system.  It's out of print, but many libraries still have it.  If not, look into its older brother, [this book](http://www.amazon.com/Principles-Neural-Science-Eric-Kandel/dp/0838577016/ref=sr_1_1?ie=UTF8&qid=1343202472&sr=8-1&keywords=kandel+fundamental+of+neural) but the sections are less digestible.
Chuck Sherrington
CC BY-SA 3.0
2012-07-25T08:45:02.197Z
@ChuckSherrington Thanks for the textbook links.
bfrs
<neuroscience><consciousness><philosophy-of-mind>
Does each sensory neuron type have a characteristic spike sequence pattern?
bfrs
# Does each sensory neuron type have a characteristic spike sequence pattern?

(Asked by: username_0 on 2012-07-22)

# Background

It is known that all sensory information is input to the brain as neural spike sequences. Now, to distinguish between the spike sequences generated by retinal red/blue/green cone cells from each other, and these from the cochlear (inner ear) hair cells, and so on, some sort of encoding scheme must be used.

To further clarify, in the case of retinal cone cells, the rate of incident light quanta in a given energy range, is the primary information that is coded. But, if all 3 types of cone cells generated identical responses for a given rate-of-incidence, like the [CCD pixels](http://en.wikipedia.org/wiki/Charge-coupled_device#Color_cameras) in our digital cameras do, then there would be no way for upstream neurons to tell what type of cone cell a spike sequence came from. Instead, my guess is that, each type of cone cell encodes the rate-of-incidence in its own characteristic way, *similar to how different types of musical instruments sound differently, even when playing the same pitch at the same intensity, via [timbre](http://en.wikipedia.org/wiki/Timbre)*.

![enter image description here](https://i.sstatic.net/di4o5.png)

[An oversimplified illustration of Timbre](http://curtismacdonald.com/harmony-and-timbre/)

# Question

**Is there evidence that each sensory neuron type has a characteristic spike sequence pattern?**

# Why message type must be encoded in the message itself

During the [development of the visual system](http://www.ncbi.nlm.nih.gov/pubmed/10888368), the retina, the LGN and the visual cortex develop separately initially and sometime later, axons from the retinal ganglions grow into LGN, and optic radiations from the LGN grow and reach into the cortex. *As far as we can tell* it is not guaranteed that a specific ganglion will project its axon to a specific neuron in the LGN. All that is guaranteed by the growth process is that ganglions close together will project to LGN neurons that are also close together.

Given this development process, when a higher region say in the V1 receives a spike stream from a neuron somewhere lower, the question arises: how does it know that this spike stream means, red, blue or green? A simple idea that occurred to me from [information theory](http://en.wikipedia.org/wiki/Information_theory) is that the message type could somehow be encoded in the message itself.

# Motivation

Evidence for characteristic spike patterns for each sensory neuron type would take us one more step towards understanding [qualia](http://en.wikipedia.org/wiki/Qualia), [the hard problem of consciousness](http://en.wikipedia.org/wiki/Hard_problem_of_consciousness). ***My speculation is that qualia are the neuronal analogs of timbre in musical instruments.***

Erwin Schrödinger thought we'd never get there. [He said](http://en.wikipedia.org/wiki/Qualia#Erwin_Schr.C3.B6dinger), *"The sensation of color cannot be accounted for by the physicist's objective picture of light [as] waves [or as quanta]. Could the physiologist account for it, if he had fuller knowledge than he has of the processes in the retina and the nervous processes set up by them in the optical nerve bundles and in the brain? I do not think so."*

I guess he's right in the sense that we will never be able to fully wrap our minds around the mysterious and ineffable nature of qualia.

However, evidence of characteristic spike patterns would offer resolutions to qualia related thought experiments, such as [Is there something about Mary?](http://en.wikipedia.org/wiki/Mary%27s_room), that philosophers seem to be [pulling their hair out over](http://ase.tufts.edu/cogstud/papers/RoboMaryfinal.htm).

**Tags:** neuroscience, consciousness, philosophy-of-mind

> **Comments:**
> **username_1**: `if all 3 types of cone cells generated identical responses for a given rate-of-incidence ... then there would be no way for upstream neurons to tell what type of cone cell a spike sequence came from.` The previous statement is false: Neurons don't just dump all their information onto one channel, they each have an axon that runs into further regions, thus up-stream neurons have information on which cone (and thus what type of cone) is sending simply by the pattern of wiring.  
> **username_2**: There is quite a bit known about vision, any intro textbook should tell you quite a bit (or even [Visual System](http://en.wikipedia.org/wiki/Visual_system)).  To be honest, I'm not quite sure what you're getting at with this question.  
> **username_1**: I agree with @ChuckSherrington I think your motivation/background is a red-herring that leaves plenty of room for questioning your question. I would remove it and try to focus on the technical part of your query. Leave the possible connections to qualia for later. Also, to avoid the comment thread swelling like it has on previous questions, feel free to [join us in chat](http://chat.stackexchange.com/rooms/2250/the-axon-terminal).  
> **username_2**: See the [Retinal Ganglion](http://en.wikipedia.org/wiki/Retinal_ganglion_cell) article on Wiki as well, that will tell you about some of the intermediate processing going on in the retina before the information is sent to the thalamus.  In general, this *is* a rate code, but it's more specific to whether the stimulus is on or off center in the field or the degree to which it is red or green (blue gets a bit more complicated).  
> **username_0**: @ArtemKaznatcheev Regarding getting meta information simply from the pattern of wiring, this is a good point and an easy mistake to make, which a few of my friends also raised. The answer is somewhat subtle, deserving of a full blog post. I'll put a link to it as soon as I've finished it.  
> **username_0**: @ChuckSherrington I have read the relevant portions from David Hubel's book, [Eye, Brain & Vision](http://hubel.med.harvard.edu/book/bcontex.htm). It does contain a ton of delightful information. Hubel was among the first to record from individual neurons in V1. However, it looks like he and other neuroscientists have overlooked this aspect. Like I have said above, evidence for characteristic spike patterns would resolve a lot of questions regarding qualia. I'll give the details in a blog post.  
> **username_0**: @ArtemKaznatcheev This question arose out of several deep meditations on qualia over the last few days and it is at the heart of my tentative explanation of qualia. If you don't like the background, simply ignore it. I'm sure a lot of people will find it very interesting and relevant.  
> **username_2**: @username_0 I think what I personally am having the hardest time with is that you're glazing over about 40 years of other research that has led to insights in this area.  I am definitely familiar with Hubel, his work was seminal.  You would probably find out with further research that there may be a reason why it was "overlooked."  The fact that things like directionality, etc., have already been established to operate by rate codes derails a substantial portion of what you claim.  I think this question may be better served in a philosophical context if you're going to ignore the existing work.  
> **username_0**: @ChuckSherrington The fact that a *rate code* is used does not in the slightest effect my claim. The *musical instrument* metaphor that I gave should make this clear.  
> **username_2**: @username_0 I'm not going to continue this discussion with you until you've read a bit more about the *actual*, *established*, scientific research in this area and you come to the table with a literature reference.  I think you've got a lot of passion about this, and that's fantastic (honest) but you need to have the basic physiological facts before you challenge the establishment with an idea.  As of right now, you're only using smoke and mirrors to do so.  
> **username_0**: @ChuckSherrington Point noted. I have been rereading Hubel and realized that I missed the bulk of the details during my earlier reading. BTW, this idea does not challenge the establishment, it is only a minor embellishment on established research.  
> **username_2**: @username_0 Try the following approach.  Set aside the color issue for now, as that complicates things for now.  Imagine a vertebrate looking at a backdrop that has a large black horizontal line drawn on it and nothing more.  Trace the image of that horizontal line from the retina, through the retinal ganglion, up to the lateral geniculate nucleus, and into V1.  This will familiarize you with the concept of receptive fields.  As you're studying the receptive fields, note the role that rate coding plays in their relay of the information through the nuclei.  
> **username_2**: con't.  See if your local library has [this book](http://www.amazon.com/Essentials-Neural-Science-Behavior-Kandel/dp/0838522459/ref=sr_1_3?ie=UTF8&qid=1343202472&sr=8-3&keywords=kandel+fundamental+of+neural) or if they can order it for you.  It has an excellent description of the visual system.  It's out of print, but many libraries still have it.  If not, look into its older brother, [this book](http://www.amazon.com/Principles-Neural-Science-Eric-Kandel/dp/0838577016/ref=sr_1_1?ie=UTF8&qid=1343202472&sr=8-1&keywords=kandel+fundamental+of+neural) but the sections are less digestible.  
> **username_0**: @ChuckSherrington Thanks for the textbook links.  

---

## 2 answers

### Answer by username_3 on 2012-07-25. Score: 5

This is an interesting idea, but I do not think it's correct. One piece of information that goes against the idea is this: auditory information is encoded by both frequency and amplitude modulation of neural spiking. The idea of spiking rate directly correlating with frequency is at odds with the idea of spiking rate containing this sort of "meta" information about the source of the activity.

We know quite a lot about how sensory information is represented in the nervous system. The simple fact of myelinated axons that don't interfere with each other already accounts for the problem you've proposed a solution for.

> if all 3 types of cone cells generated identical responses for a given rate-of-incidence... then there would be no way for upstream neurons to tell what type of cone cell a spike sequence came from

Here I believe is where you've made an error. The transmission of activity from the sensory neuron itself to an upstream neuron inherently conveys information about the sensation. The firing of the sensory neuron is a translation of the external phenomena to an internal neural code. No extra information is needed to represent the source of the activity.

**References**

Li Liang, L., Lu, T., & Wang, X. (2002) [Neural Representations of Sinusoidal Amplitude and Frequency Modulations in the Primary Auditory Cortex of Awake Primates](http://jn.physiology.org/content/87/5/2237.full.pdf+html). *J. Neurophysiol* 87:2237-2261.

> **Comments:**
> **username_2**: This is surely more effective than the 5 page tome on the visual system I was thinking about writing! Nice work.  
> **username_0**: Your description of the auditory system seems to be at odds with what I've read elsewhere, [von Bekesy's Place Theory](http://en.wikipedia.org/wiki/Georg_von_B%C3%A9k%C3%A9sy), which essentially says that the cochlea does a **Fourier transform** of the input pressure wave recorded by the eardrum. Also, I feel you have missed the problem I'm describing, here's another attempt: If red/blue/green are all converted to the same neural code, a rate coded spike stream, how do upper regions know which is which?  
> **username_3**: @username_0 Auditory physiology has advanced significantly since Bekesy. The paper I linked shows this, and you can find many more on the same subject. I do not believe I have misunderstood you. You're not considering that the individuality of neurons is itself a type of encoding. The upper regions know which is which because different retinal ganglion cells (simplification here) respond to different colors. When a green/red ganglion cell fires, it is informing the upper regions that there is green/red within that place on the retina. No extra information needs to be encoded in the firing rate.  
> **username_0**: @username_3 Thanks for responding. Ok, here's where I keep getting confused: What if right after the green/red ganglion's firing, a blue/yellow ganglion right next to it fires...how does the upper region know its not another (or the previous) green/red one firing a second time?  
> **username_3**: @username_0 Because each ganglion cell has it's own axonal projection to the LGN. The LGN is more or less a topographical map of ganglion cells, so the information is preserved.  
> **username_0**: @username_3 I guess I have some reading to do to understand how the LGN creates its topographical map. Any suggestions for a good source of reading material?  
> **username_0**: @username_3 I hope you have not missed the new section I added to the question: **Why (I think) message type must be encoded in the message itself**  
> **username_3**: @username_0 Start thinking in terms of activity. That is what counts. The neurons can be considered conduits for this activity. Activity generated by some external happening travels into the nervous system, and that activity inherently represents what caused it. That is the foundation of the functioning of the nervous system, and it can be a little difficult to digest. Here is one more example to clarify: how does the nervous system differentiate between a touch on the toe and on the finger? Because the sensory neurons in the toe *inherently* represent activity there. No need to code the location.  
> **username_0**: let us [continue this discussion in chat](http://chat.stackexchange.com/rooms/4263/discussion-between-username_0-and-preece)  

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### Answer by username_0 on 2012-07-26. Score: -2

After an *eye opening* experience rereading Hubel's book, [Eye, Brain & Vision](http://hubel.med.harvard.edu/book/bcontex.htm) and a bunch of papers, I found that the answer to my question is a superficial *yes* and a strong **no**.

It is unsurprising that [neuroscientists have investigated](http://www.ploscompbiol.org/article/info%3adoi/10.1371/journal.pcbi.1000433) if there are analog characteristics to neural spike streams:

> Neurons communicate with each other using stereotyped electric pulses,
> called spikes. It is believed that neurons convey no information
> other than the frequency of the transmitted spikes, called the firing
> rate. However, it is possible that neurons may communicate some
> information through the finer temporal patterns of the spikes because
> biological, as well as electrical/mechanical signals generally reveal
> internal conditions of the signal generator...
>
> ... First, we found that
> neurons exhibit stable firing patterns that can be characterized as
> “regular”, “random”, and “bursty”. Second, we observed a strong
> correlation between the type of signaling pattern exhibited by neurons
> in a given area and the function of that area.

So, in a superficial sense the answer is yes, sensory neurons might have characteristic firing patterns. However, when it comes to transmitting generic analog signals, neurons have one big handicap: ***any analog features in the signal are lost at synaptic junctions, where the electrical signal is transformed into a chemical message.***

One way to preserve at least part of the analog information, say message type encoded in a characteristic pattern, might be to have the message transmitted over *a sequence of neurons of the same size and type which all fire in a similar way*. However, in the visual system, there is no evidence for this. The retinal ganglion cells have their axons end in the LGN whose neurons are very different, and these in turn send their spikes to V1 whose neurons are again different. So, any characteristic patterns generated by the ganglions are lost in the LGN synapses.

The bigger question still remains: how do upper regions figure out what type of ganglion is sending the spike stream? (I'll formulate this more properly as a separate question).

> **Comments:**
> **username_1**: to your final question. Did you spend time thinking [about my comment](http://cogsci.stackexchange.com/questions/1455/does-each-sensory-neuron-type-have-a-characteristic-spike-sequence-pattern/1476#comment2649_1455). The key part of neural-networks is their wiring pattern, I recommend reading a bit of wikipedia before follow up questions, though.  
> **username_0**: to whoever downvoted, could you comment on what you found wrong with my answer.  
> **username_0**: @ArtemKaznatcheev instead of the blog post promised, I added a new section to the question. In essence what I'm trying to convey is that unlike a human designed NN or chip where the wiring is completely pre-specified, in the brain, the genetic code does not seem to do this.  
> **username_1**: there are plenty of NN where the wiring is not specified initially. Why don't you look up the cascade correlation algorithm or some of the questions I asked. Making significant edits to a question after it has been answered is considered poor form.  
> **username_2**: `How do upper regions figure out what type of ganglion is sending the spike stream?` Receptive fields.  Neurons with one type of receptive field in the retina are mapped onto those with a similar receptive field in the thalamus (the notion of topography that username_3 mentions) which map onto neurons with a similar receptive field in higher centers.  I reaffirm that a bout with a good textbook will open these worlds up to you.  

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