Glial Cells as Perceivers of Musicality
I have, for quite a long time, proposed that glial cells play a major role in the perception of music.
The rationale for this hypothesis is that:
- Pitch scales and nested regular beat are musical features that would be expected to cause constant activity patterns in corresponding cortical maps, where the constraints determined by those musical features (when listening to a particular musical item) cause each of those cortical maps to be divided into a set of active neurons and a set of inactive neurons. (The simplest example of this is in a cortical map that represents information about pitch, where neurons representing pitch values in the scale are active, and neurons representing pitch values not in the scale are inactive.)
- These patterns of activity relate to the actual physical location of active and inactive neurons in a cortical map, and this suggests the existence of some type of “meta-perception” of the activity of neurons as a function of their location. That is, if musicality is determined by the occurrence of the constant activity patterns, then there has to be something in the brain that is observing the occurrence of those patterns.
- Glial cells are a plausible candidate for the something doing the observing, because glial cells interact with neurons as a function of their proximity to those neurons.
- That is, I propose that there are glial cells located in cortical maps that relate to the perception of musical sound, and those glial cells are responsible for “observing” the musicality of music as defined by the occurrence of these constant patterns of neural activity.
Evolution of the Musical Glial Cell Theory
My development of this theory has taken place over a period of time, and even now I remain uncertain about basic aspects of the theory.
A brief history of the main ideas is as follows:
- https://whatismusic.info/chapters/whatismusic-14-final-theory.pdf - here I presented the concept of constant activity patterns. But at this point I had not yet had the idea that glial cells were involved – I speculated about the existence of a “musicality neuron” that was able to detect and respond to the occurrence of constant activity patterns.
- https://whatismusic.info/blog/MusicalityBrainCells - here I developed the idea that the musicality-detecting brain cells were actually glial cells, not neurons, based on the observation that glial cells are associated with neurons as a function of physical proximity to those neurons.
- https://whatismusic.info/blog/MusicIsThingsThatHappenAndThingsThatDontHappen.html – this is an attempt to better explain the constant activity patterns theory.
- https://whatismusic.info/blog/TheGlialIllusionHypothesis.html - here I presented a variation on the theory that not only do glial cells play a major role in the perception of musicality, but that music is itself a type of illusion, in effect “tricking” glial cells into thinking that something is true which isn’t.
- https://whatismusic.info/blog/TheFundamentalBuildingBlockOfMusicIsExactRepetition.html - here I restated the theory of glial perception of music in terms of the response to exact repetition. (One thing missing from this restatement was the identification of constant activity patterns with exact repetition, in the sense that the things being exactly repeated correspond to the active portions of the constant activity patterns in the cortical maps responding to those things being exactly repeated. So it’s not that I decided that the concept of constant activity patterns was wrong, but more that I realised it could be restated in terms of the exactness of repetition.)
- https://blog.thinkinghard.com/blog/music-emotional-response-vs-pragmatic-response/ - here I arrived at my current theory of musical emotion, mostly based on an analysis of the nature of song lyrics.
- https://blog.thinkinghard.com/blog/evolutionary-origin-of-music/ - considering how the previous item fits into evolutionary theory, I came to the conclusion that music perception is or was fairly functional – and this suggested that perhaps my earlier idea of music being an “illusion” was not so relevant (in as much as an illusion is by definition a result of perceptual processing that results in a false and therefore non-adaptive perception of something).
Glial Cells as Deciders to “Not Bother Trying”
As mentioned in the last two items in the previous list, I have fairly recently developed a hypothesis that our emotional response to song lyrics has two major aspects:
- Responding to the emotional consequences of a situation that a protagonist finds themselves in.
- Not bothering to try and think about how one might deal with such a situation.
At the time of developing this hypothesis, I was not particularly thinking to relate it to any hypothesis about glial cells.
However, I recently came upon this article from Quanta Magazine.
It described three different papers about the roles that astrocytes (one type of glial cell) play in the brain.
One paper was Glia Accumulate Evidence that Actions Are Futile and Suppress Unsuccessful Behavior, which reported an observation that glial cells are directly involved in decisions to “give up” when repeated attempts to do something fail.
I realised that this is similiar to, albeit not exactly the same as, the second component of my hypothesis about how the human brain responds to song lyrics, ie music causes the listener to not bother to think about how one might deal with a situation.
The similarity is apparent if we describe both scenarios in terms of an individual “not bothering”.
That is:
- As glial cells accumulate evidence that actions are futile, the individual animal will decide to give up, that is, not to bother trying anymore.
- According to my hypothesis about the response to song lyrics, the listener decides not to bother trying to think of how one might deal with the situation described in the lyrics.
The main difference between the two scenarios is that in the “giving up” scenario the individual eventually decides not to bother trying, whereas in the musical scenario the “not bothering to try” happens straight away.
Possible inter-glial cell communication involved in our response to music lyrics
If glial cells can be involved in deciding “not to bother”, and if glial cells are involved in the perception of musicality, then it is quite possible that the connection between these two things occurs via a connection from one set of glial cells to a different set of glial cells – without there being any intervening communication or processing involving neurons.
That is, something like:
- Neurons in certain cortical regions perceive music, and the features of music cause certain patterns of activity in those regions.
- Glial cells in those regions perceive those patterns of activity.
- Those glial cells respond to the perception of these patterns by transmitting a “don’t bother trying” signal to other glial cells.
- The glial cells that receive the “don’t bother trying” signal are in regions containing the neurons that would otherwise think about how to deal with a situation, and those glial cells deactivate those neurons.
Glial processing of musical information is probably very low bandwidth
I have proposed that glial cells play an important role in how the human brain processes and responds to music.
But, at the same time, I am not suggesting that glial cells can somehow process information in a manner analogous to what neurons are capable of, where large amounts of information are processed at a relatively high speed.
In fact my theory as proposed so far implies that the musical information processed by glial cells consists entirely of a single 1-dimensional quantity, which we might label as the “musicality” of the music – that is, how musical is the music (or supposed music) being listened to.
We can imagine “musicality” as being represented by a number from 0 to 10, where 0 is not musical at all, and 10 is your favourite music, and 3 is sort-of-musical but not very good, and 5 might be not that great but something that you can listen to.
To put it another way, your glial cells do not “know”:
- Whether you are listening to jazz or heavy metal or classical music.
- Whether the tune is in a major key or a minor key.
- Whether it’s in 3/4 or 4/4 time.
- Whether the emotions expressed are sad or happy.
The only thing that they know is:
- The musicality: how good is the music?
Your glial cells won’t even know which emotion the music expresses, but the perceived musicality will determine the intensity of the emotional feeling that you experience when listening to the music.
Without the relevant glial cell circuits, your brain would completely fail to respond to music, but, at the same time, it’s the neurons that are doing almost all of the detailed work required for your brain to process musical information.