The Glial Illusion Hypothesis

Illusions

An illusion is a false perception. An illusion usually happens when your brain is presented with a contrived stimulus, and the neurons in your brain process sensory information from that stimulus, and they generate a perception, but the perception is incorrect.

Our brains are the result of millions of years of evolution, and they have evolved to correctly process all or almost all of the sensory information that they receive from naturally occurring stimuli.

But evolution does not guarantee that an evolved system will produce a perfectly correct answer all the time. Evolution only requires that the system produce a good-enough answer most of the time.

With a sufficient level of contrivance, it is possible to create stimuli which lie outside the range of naturally occurring stimuli that our brains have evolved to process correctly.

The incorrect perceptions generated in response to these contrived stimuli are what we call "illusions".

In most cases we are consciously aware of the incorrect perception, and at the same time we can be presented with evidence which demonstrates objectively that the illusory perception is indeed false.

For example, a picture might be presented, and it has lines that look like they have different slopes, but then you get your ruler and your protractor out and you determine that the lines are all indeed parallel.

Or you look at a pattern printed out on a piece of paper and it looks like the lines in the pattern are moving but you know that it's just a pattern printed on a piece of paper, so the lines can't be moving.

Neurons and Glial Cells

Roughly half of the cells in our brains are neurons.

To a first approximation we can say that neurons are the brain cells that do all the information processing that happens in the brain. Neurons receive information from our senses, and they output information to our muscles (and also a few other places like our glands), and our brains contain a whole lot of neurons all receiving information from and sending information to each other.

Neurons are involved in all the processes of observation with regard to things happening in the world, and also with regard to things happening in our bodies outside of our brains.

Almost all known illusions represent incorrect outputs from computational processes carried out by neurons.

All the other cells in the brain are classified as glial cells.

Glial cells serve various functions, and most of those functions relate to the support, maintenance and regulation of neurons.

We can think of neurons as being "the talent", and glial cells are like all the people required to support and help the talent, without which the talent couldn't actually do what it does.

As part of doing their job of supporting, maintaining and regulating neurons, glial cells necessarily have to observe the activity and state of the neurons that they are supporting, maintaining and/or regulating.

Given that illusions can be defined as the failure of information processing involved in the observation of something, and given that glial cells necessarily observe the state and activity of neurons, it follows that we can consider the possibility that "glial illusions" can be a thing.

In particular, a contrived pattern of neural activity could cause some set of glial cells to generate a false perception of the state or activity of some set of neurons, and this could in turn result in the incorrect regulation of those neurons.

With a glial illusion there is an extra degree of indirection.

Firstly, in order to contrive a particular pattern of neural activity, it is necessary to contrive a perceptual stimulus which invokes that particular pattern of neural activity, and then that pattern of activity is the stimulus which causes the glial cells to incorrectly perceive what is happening. (It should be noted that there is not necessarily any illusion happening at the neural level. That is, the consciously perceived qualities of the contrived stimulus do not include any false information about that stimulus.)

Secondly, the result of the incorrect glial perception will not be a specific conscious perception that the person is aware of, because glial cells do not output information that is directly available to conscious perception. If the glial illusion results in dysregulation of neural activity, then the person will be indirectly aware of the effect of this dysregulation, and they might conclude that the original contrived stimulus has somehow caused them to develop an altered state of mind.

To put it another way, the glial illusion will not cause the person to "know" something that isn't true, but it will cause them to "feel" different somehow, where the feeling in question does not seem to be obviously related to the contrived stimulus that is causing it to occur.

Music Could Be a Glial Illusion

Could music be a glial illusion?

There are a various reasons why it is both possible and at least plausible that music is a glial illusion.

1. The Unsolved Mystery of Music

The first reason is that nobody actually knows what music is.

Science has had hundreds of years to study the problem.

And the current status of scientific understanding of music is that noone has any idea why a thing like music should exist at all.

I think it's fair to say that music science is in desperate need of some new ideas, and the final answer to the mystery is likely to be something quite different to all the theories that everyone has thought of so far.

2. Biological Function, or lack thereof

There is no convincing evidence that music has any biological function.

One thing about illusions is that the illusions themselves are not functional.

The mechanisms of perception serve a function when they generate correct answers.

Illusions are what happen when the mechanisms of perception generate incorrect answers.

In other words, illusions are evidence of biological dysfunction, which is the exact opposite of biological function.

3. Music shows evidence of Contrivance

Music consists of patterns of sounds constructed from various components, like melody, and harmony, and rhythm.

Music is not particularly like anything else. Music has melodies, which are constructed from scales. Music has rhythm, which is constructed from what we might call nested regular beats – ie bars, notes within each bar, fractional notes within the notes (so, for example, a rhythm based on regular 4/4 time with quarter notes, will have beat periods of 4 notes, 2 notes, 1 note, 1/2 a note and 1/4 of a note, which is five distinct beat periods).

These aspects of music are peculiar to music, and do not occur in any other phenomenon that humans normally have occasion to perceive.

To get the full effect, music has to be constructed or performed quite precisely – music played out-of-tune or out-of-time does not provide a satisfactory experience to the listener.

These general properties of unique peculiar characteristics combined with a required precision of construction are typical of many illusions, especially visual illusions, many of which need to be generated by software. (For example, I don't think anyone can easily produce a working version of the Pinna-Breistaff illusion from a freehand drawing.)

4. Music shows Abstract Similarities across different Aspects

As already mentioned, music has different aspects, such as melody and rhythm, and each of these is constructed from specific features, including melodic scales and nested regular beat.

For both scales and nested regular beats, each of these is defined by things that happen and things that don't happen.

In the case of scales, the things that happen are the pitch values of the scale, and the things that don't happen are the pitch values between the pitch values of the scale.

In the case of nested regular beat, the things that happen are the nested beat periods (for example the five beat periods identified above for 4/4 time with quarter notes), and the things that don't happen are other beat periods.

This phenomenon of "things that happen and things that don't happen" has an obvious interpretation in terms of neural activity, which is: neurons that fire and neurons that don't fire.

And because this pattern occurs across different aspects of the stimulus, ie music, this implies the occurrence of same or similar patterns of neural activity across different cortical maps.

And where different cortical maps have similar patterns of neural activity, it is reasonable to suppose that glial cells in those different cortical maps will have similar responses to those similar patterns of neural activity.

And if the glial response is an illusory response, due to the contrived nature of those neural patterns of activity, then this illusion and the consequent neural dysregulation will be occurring across multiple cortical maps.

Propagation of the Glial Illusion

One important aspect of music is that the stimulus and the final effect are apparently separated, and this is something that needs to be explained.

A musical stimulus consists of patterns of sound, and aspects of sound such as pitch and the rhythm, which are perceived and processed in various areas in the auditory cortex.

The observed effect of music on the state of mind of the listener has to do mainly with emotions and feelings of various kinds.

If we suppose that the effects of glial illusions are purely local, then this hypothesis will fail to explain how the perception of certain sounds, which occurs in one part of the brain, ie the auditory cortex, can possibly influence the perception or experience of emotion, which occurs in some other part or parts of the brain.

To make the hypothesis work, it is necessary that the affected neural regulation not be purely local.

The propagation of neural dysregulation might, for example, just be indiscriminately global. Ie the glial illusion occurs, triggered by an auditory stimulus, and the consequent neuronal dysregulation occurs throughout multiple areas in the brain.

Or, there may be some directional propagation, whereby the neuronal dysregulation follows the path or "pipeline" of normal information processing.

For example, it might propagate along the following information processing pathway:

1. Perception of sounds =>
2. perception of speech sounds =>
3. perception of words and syntax =>
4. perception of meaning of speech =>
5. emotional response to the perceived meaning of speech.

So the dysregulation propagates (somehow) so that the contrived patterns of neural activity in item 1 cause downstream dysregulation of neural activity in item 5.

(Here I am assuming that the relevant glial response to neural activity is propagated along a pathway that matches the pathway that travels from raw sound perception via speech perception to emotional response, even though, in the case of music, there isn't necessarily any speech perception happening. In other words the glial connections exist because quite often neural activity transmits information along that pathway, and the glial connections remain active whether or not neural activity is processing and transmitting that particular type of information on that particular occasion.)

A More Detailed Hypothesis

Requirements

My hypothesis about music, as so far stated, is fairly abstract.

I am asserting that music generates some particular patterns of neural activity which cause some kind of false perception in glial cells, which results in some kind of incorrect regulation of neural activity. (And also that, somehow, this dysregulation is propagated to neurons outside those brain regions where those glial mis-perceptions occurred.)

To develop this hypothesis into a full theory of music, we need to fill in all the details, and in particular we need to answer the following questions:

• What are the features of music, as a contrived stimulus, that result in the specific patterns of neural activity?
• What are those patterns of neural activity?
• What aspect of the neural activity is the relevant set of glial cells observing?
• What aspect of neural activity is being regulated by the glial cells, and how does that relate to the observations in question?
• What is the incorrect perception of neural activity that results from the contrived musical stimulus?
• What type of dysregulation is caused by this incorrect perception?

With regard to the issue of propagation to areas of the brain beyond the locations where the glial mis-perceptions generating dysregulatory responses originally occurred, we need to answer the additional following questions about how such regulatory responses are or could be propagated:

• Are they propagated across the inter-cellular environment?
• Are they propagated indiscriminately to all or most other brain regions?
• Are they propagated through connections between different glial cells?
• If such connections exist between glial cells in different brain regions, do they mirror the general flow of information between the co-located sets of neurons in each case?

Even now, our understanding of all the interactions that occur between neurons and glial cells is limited, and it is only fairly recently that scientists have started to realise how much glial cells are involved in the real-time information processing that occurs within the brain.

It follows that, in my attempts to formulate a detailed hypothesis about music as a form of glial illusion, I am going to have to make various ad hoc assumptions about such interactions between glial cells and neurons that may exist.

Some of the specific assumptions I make might turn out to be wrong, for example as a result of increased scientific understanding of those interactions.

However the incorrectness of any such specific assumptions would not necessarily disprove the overall hypothesis (ie that music is a glial illusion), albeit they would require revision of the aspects of the more detailed hypothesis depending on those specific assumptions.

And having said that, I now present a tentative more detailed hypothesis about how music could be a glial illusion.

Detailed Hypothesis: Fading out Old Information to Make Room for New Information

Let us suppose the existence of a set of neurons, located in some region of the brain, where the activity of those neurons represents the occurrence of events with particular perceptual values as they occur, and different neurons represent different perceptual values, in such a manner that a neuron representing a particular perceptual value becomes active when the event with that perceptual value occurs, and continues to be active for some short period of time afterward.

Therefore, the activity of one neuron represents either:

• The event with the corresponding perceptual value is happening right now, OR,
• The event happened a short time ago.

To distinguish between "right now" and "a short time ago", we might further suppose that the initial neural activity changes somehow as time passes. For example, the level of activity might decay at a certain rate.

(Typically such neurons would belong to a cortical map, where there is some correlation between the position of a neuron in the map and the perceptual value that it represents. This is somewhat of a simplification, because it ignores the whole phenomenon of population encoding, where a perceptual value is actually represented by the activity of multiple neurons, and the represented value is an average of the values that those individual active neurons each represent. But I will ignore this complication for the moment.)

The question then arises, what is the ideal rate of decay for the activity of such a neuron in response to the occurrence of a single event?

If the decay is too slow, and there are too many events being perceived, then eventually all of the neurons will become maximally active, and the activity will never decay back down to the minimal base level.

A cortical map best represents information about something when some neurons are active and some neurons are not active at any moment in time. So it is undesirable for all the neurons to be fully active at the same time, and it is also undesirable for all or most of the neurons to be inactive at any time.

Also, if the decay is too fast, and there aren't that many events being perceived, the result will be that information is being discarded too quickly. In cortical maps where neurons represent different perceptual values occurring at different times, the relationships between different values occurring at different times are important.

For example, if neuron X responds to event 1 at time T₁ and neuron Y responds to event 2 at later time T₂, and if the activity of neuron X in response to event 1 has already decayed to zero at T₂, then other neurons connected to both neuron X and neuron Y will not have the ability to respond to the relationship between event 1 and event 2, because neuron X will have ceased providing information about event 1.

So we don't want the decay rate to be too slow, and we don't want the decay rate to be too fast. And the optimal decay rate for neural activity within such a cortical map will be strongly tied to the rate at which new events are being perceived within that cortical map.

That is, if new information comes in more quickly, then the decay should happen proportionately faster, and if new information comes in more slowly, then the decay should be proportionately slower.

Determining what this optimal decay rate should be, based on observation of overall patterns of activity in a cortical map, is just the job that we might expect glial cells to do.

In other words, we might expect that glial cells would regulate the rate of decay of neural activity provoked by individual perceived events as a function of the rate at which new events occur as perceived by the glial cells.

So, in order to perform this type of regulation, the glial cells will have to do two things:

1. Perceive the rate at which information about new events is coming in.
2. As a function of that perceived rate of new information coming in, release or emit a control signal that controls the decay rate of activity of the neurons that they are regulating.

Implementation of the second item is probably straightforward enough – the control signal could consist of some messenger molecule that is released into the cellular medium, and which acts on neurons so as to increase or decrease the decay rate accordingly.

Implementation of the first item requires the glial cells to estimate the rate of events being responded to by the neurons, by directly observing the activity of those same neurons.

One way to estimate the rate of new events being responded to is to observe how often a neuron goes from inactive to fully active. Now, because neural activity decays gradually, sometimes a neuron will be re-activated without first fully fading to an inactive state. However, in most situations, all of the neurons in a cortical map will become inactive some of the time, and therefore a corresponding portion of new events will involve activation from inactive to fully active.

So measuring the rate at which neurons go from inactive to fully active is a reasonable proxy for estimating the rate at which new information comes in.

And for the perception of most natural phenomena, this proxy is probably a very good proxy, because most natural phenomena do not involve exact repetition of the perceptual values of the events generated by the perception of that phenomenon in each case.

However, it could be possible to contrive a stimulus which breaks the assumption underlying this method of estimation, where the stimulus contrived would involve an unnatural level of exact repetitions of perceptual values.

Such a contrived stimulus would activate the corresponding cortical map of neurons in such a manner that one subset of neurons is never activated, and at the same time, another subset of neurons is constantly re-activated, such that neurons in the second subset never fully decay their activity back to the minimal base rate of activity (and where the second subset consists of those neurons that represent the perceptual values which are being exactly repeated by the stimulus).

As a result of such a contrived stimulus, the glial cells would underestimate the rate at which new events are being processed, and consequently they would regulate the decay rate of activation of the neurons down to a minimal value. That is, they would allow neural activity of the active neurons to persist to a maximum extent, even though information about new events was actually coming in at a rate higher than what the glial cells estimate, and for which the optimal decay rate would be higher than the regulated minimal value.

This then, according to my proposed detailed hypothesis, is the glial illusion, and the resulting persistence of activation is the consequent dysregulation.

Propagation

This detailed hypothesis does answer the questions in the first list above, but, we still need to answer the second set of questions about propagation.

That is, is there some good reason for this type of regulation of neuronal activity to be propagated "downstream" of the original cortical map?

I would tentatively answer "yes" to this question, based on assumptions about how all this might relate to the processing of speech.

To summarise my detailed hypothesis as state so far – music creates a glial illusion which causes a false perception of a low rate of incoming events being processed, which in turn causes dysregulation of the decay rate of neural activity, resulting in neural activity persisting more than it should (or normally would).

The sounds of music are somewhat similar to the sounds of speech, and speech is one thing that can happen at different speeds, and where the brain needs to adapt its processing to match the speed of incoming audio perceptions. (Speech can happen at different speeds for the simple reason that different people talk at different speeds on different occasions.)

It follows that there is likely a need for regulation of how neurons process information when processing speech, based on perception of how fast the speech is occurring, and this regulation would apply to the processing of the speech itself, and to the processing of information derived from the speech, ie the meanings of what has been said.

So it is plausible that this type of regulation does occur in cortical maps of neurons involved in processing the sounds of speech and music.

It is also plausible that the speed of processing for information downstream of speech also needs to be regulated similarly, and it is possible that such regulation can be driven, or at least partly driven, by the glial perception of neural activity in the upstream cortical map where the audio events are being processed.

We can regard speech as a system whereby a speaker constructs "thoughts" in the mind of the listener.

Thoughts are basically imaginary perceptions, and one thing we know about imaginary perceptions is that they are represented by the activity of the same neurons which represent real perceptions. For example, the neurons that "think" the colour blue of an imaginary blue thing are the same neurons that "see" the colour blue of a real blue thing.

The only difference between imaginary and real is that neural activity representing imagined things occurs at a lower intensity.

This raises the possibility that neural regulation of neural activity relating to "thinking" could involve targeting all such neurons based purely on the reduced intensity of activity that occurs when "thinking", and therefore the regulatory messenger molecules could be globally broadcast to all regions of the brain, ie, without having to "know" specifically which brain regions are having the thoughts derived from any particular fragment of speech.

In other words, the perception and regulation of neural activity of neurons involved in the processing of speech and the meaning of speech would occur as follows:

• Glial cells in auditory processing regions observe the rate at which new auditory events come in.
• In response to the observed rate of new events, the glial cells emit one or more control substances that control the rate of decay.
• These control substances form a signal which is distributed indiscriminately across a substantial part of the cortex, and this signal only acts on those neurons that are in "thinking mode", ie which have a level of activity and a recent history of activity that corresponds to "thinking" and not to the actual perception of real things.

In the case of glial illusion and consequent dysregulation:

1. Glial cells in auditory processing regions incorrectly perceive a low rate of new auditory events.
2. Those glial cells release (or perhaps don't release) a control substance so that the rate of decay is minimised.
3. Neurons in "thought mode" respond to this decay minimisation signal, and as a result they maximally persist their level of activity.
4. As a result of this heightened persistence, emotional responses to the corresponding thoughts are increased in intensity.

The end result is that the perception of music heightens the listener's emotional response to their own thoughts.

History

As early as 2005 I came to the conclusion that glial cells might be involved in the perception of the 'musicality' of music.

However, at that time, and for the 18 years since then, I assumed that this was part of an adaptation.

I assumed that if some set of glial cells had the job of perceiving the musical quality of music, then this "job" must be some kind of adaptation, one that had evolved because the adaptation somehow increased long-term reproductive success.

It is only in the last few weeks that I have come to realise that it doesn't have to be an adaptation - that music has abstract similarities to many known illusions, and illusions are not adaptations, and if it's the glial cells that perceive music, and music is an illusion, then that means music is a glial illusion.

Which makes music a very unique type of illusion, because all other known illusions are, as far as anyone knows, "neuronal" illusions.