<p>In this article, <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6618409/" rel="nofollow noreferrer">Broadband Cortical Desynchronization Underlies the Human Psychedelic State</a>, this sentene is said:</p>
<blockquote>
<p>Psilocybin reduced spontaneous cortical oscillatory power from 1 to 50 Hz in posterior association cortices, and from 8 to 100 Hz in frontal association cortices.</p>
</blockquote>
<p>I'll abbreviate posterior association cortices to <em>PAC</em>, and frontal association cortices to <em>FAC</em>.</p>
<p>As found out in this <a href="https://psychology.stackexchange.com/questions/26587/is-the-oscillatory-power-inversely-proportional-to-the-frequency/26588#26588">question</a>, the above sentence really means that after psilocybin intake, the brain waves present in the PAC are high-level gamma frequencies, and the brain waves present in the FAC are delta and theta frequencies. They are the ones left, since the other bands were desynchronized away.</p>
<p>Now, since these are the bands left, does that mean that they are more prevalent? Does that mean that the PAC will be operating fully on high-level gamma frequencies and therefore there'll be more of these frequencies in the PAC than usually?</p>
<p>If so, does this mean that the senses of which the PAC is responsible for, will be <strong>heightened</strong>, since the gamma frequency is a higher frequency, meaning more information is passed in less time? And does that mean that the senses of which the FAC is responsible for, will be <strong>diminished</strong>, since the delta and theta frequencies are the lowest?</p>

CC BY-SA 4.0
2021-02-02T21:00:58.043Z
"They are the ones left, since the other bands were desynchronized away." - that's not actually what the paper from the last Q&A said. These are places and bands where there was a *significant decrease* in power. You do not know that the other bands are "left", just that they are not significantly decreased. It could be, for example, that power started low in those bands, and so there was nothing to decrease. It could be that power was high in bands that decreased, so now they are more similar. Also decrease in power is not necessarily the same thing as "desynchronization".
Bryan Krause
CC BY-SA 4.0
2021-02-02T21:48:29.313Z
@BryanKrause Okay, thank you for the clarifications. A little later in the article, this is said: "In bilateral prefrontal cortices, the decreased power (“desynchronization”) ranged from alpha (8–13 Hz) to high gamma (50–100 Hz)." Because of this I assumed they were talking about a decrease of power via desynchronization at all times, but that may be innaccurate. This is the only sentence I saw them clarify it as "desychronization", so it could be that it only applies to the bilateral prefrontal cortices.
A. Kvåle
CC BY-SA 4.0
2021-02-02T22:05:32.857Z
This paper is using that term. They should not, and you shouldn't carry it with you.
Bryan Krause
CC BY-SA 4.0
2021-02-02T22:07:38.313Z
@BryanKrause So desynchronization doesn't usually lead to a decrease in oscillatory power? Or, something else is usually behind a decrease in oscillatory power?
A. Kvåle
CC BY-SA 4.0
2021-02-02T22:12:10.667Z
Desynchronization is a possible cause of power decreases in EEG because you can imagine each EEG recording as originating from the sum of many small nodes over some region of the brain near the contact. If those sources are in sync, they will sum. If they are not, some may cancel others out. However, you can also have power changes if individual nodes change amplitude. Separately, desynchronization is also used to refer to the whole broadband EEG, in which "synchronized" refers to brain states in which low frequency power is high (like slow wave sleep) and "desynchronized" is like wake.
Bryan Krause
CC BY-SA 4.0
2021-02-02T22:13:41.040Z
The authors here may be trying to associate psychedelics with a "more awake than awake" brain state, and they're linking those two types of synchronization in doing so. There are some data that support this general idea, but I don't think that should apply to the data they present in this particular paper.
Bryan Krause
CC BY-SA 4.0
2021-02-02T22:21:10.137Z
@BryanKrause In response to your third comment: I'm having trouble understanding the last sentence you wrote. So, desynchronization can be used to imply awakeness? Could you elaborate how this meaning arose?
A. Kvåle
CC BY-SA 4.0
2021-02-02T22:39:40.117Z
The meaning arose because when you are asleep, you have a "slow", synchronized EEG (synchronized in this context meaning lots of slow, low-frequency power). As a bit of an exaggeration, imagine a brain where every neuron oscillates together, from being inactive and hyperpolarized, to a second later being active and depolarized. Slow wave sleep is close to this state. There's very little information in this state, and little information processing if everything is just oscillating together slowly. Wake is very far from this state.
Bryan Krause
CC BY-SA 4.0
2021-02-02T22:49:15.013Z
@BryanKrause I think I understand: In this second sense, "desynchronization" would be taking a very simple system (a bunch of synchronized, low-frequency neurons), and making it more complex and chaotic. Whereas, in the other sense, desynchronization refers to  the neurons within an ensemble not firing togetherh, and therefore not providing oscillatory power to the band they would usually strenghten. As far as I've understood it, certain ensembles have frequencies they usually abide by, different  parts receiving different types of sensory input, communicate with gamma freq. to bind the info.
A. Kvåle
CC BY-SA 4.0
2021-02-02T22:56:54.380Z
Yep, that sounds right, up until the gamma binding bit. High gamma activity tends to be correlated with spiking activity, as well as fMRI BOLD signals. I think that's all pretty non-controversial. Besides that, there are many theories. There's a gamma binding hypothesis, which you refer to, though I hear less about that lately. There are theories about gamma being a "feed-forward" and beta (or maybe alpha) being a "feed-back" rhythm, with modest support. Authors of different papers will mention one theory or another but it's all very much under investigation.
Bryan Krause
CC BY-SA 4.0
2021-02-02T23:05:20.960Z
@BryanKrause Very interesting all of this, thank you for all the information :)
A. Kvåle
<sensory-perception><brain-waves>
Does the desynchronization of some bands mean an increase in the prevalence of the other bands?
A. Kvåle
# Does the desynchronization of some bands mean an increase in the prevalence of the other bands?

(Asked by: username_0 on 2021-02-02)

In this article, [Broadband Cortical Desynchronization Underlies the Human Psychedelic State](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6618409/), this sentene is said:

> Psilocybin reduced spontaneous cortical oscillatory power from 1 to 50 Hz in posterior association cortices, and from 8 to 100 Hz in frontal association cortices.

I'll abbreviate posterior association cortices to *PAC*, and frontal association cortices to *FAC*.

As found out in this [question](https://psychology.stackexchange.com/questions/26587/is-the-oscillatory-power-inversely-proportional-to-the-frequency/26588#26588), the above sentence really means that after psilocybin intake, the brain waves present in the PAC are high-level gamma frequencies, and the brain waves present in the FAC are delta and theta frequencies. They are the ones left, since the other bands were desynchronized away.

Now, since these are the bands left, does that mean that they are more prevalent? Does that mean that the PAC will be operating fully on high-level gamma frequencies and therefore there'll be more of these frequencies in the PAC than usually?

If so, does this mean that the senses of which the PAC is responsible for, will be **heightened**, since the gamma frequency is a higher frequency, meaning more information is passed in less time? And does that mean that the senses of which the FAC is responsible for, will be **diminished**, since the delta and theta frequencies are the lowest?

**Tags:** sensory-perception, brain-waves

> **Comments:**
> **username_1**: "They are the ones left, since the other bands were desynchronized away." - that's not actually what the paper from the last Q&A said. These are places and bands where there was a *significant decrease* in power. You do not know that the other bands are "left", just that they are not significantly decreased. It could be, for example, that power started low in those bands, and so there was nothing to decrease. It could be that power was high in bands that decreased, so now they are more similar. Also decrease in power is not necessarily the same thing as "desynchronization".  
> **username_0**: @BryanKrause Okay, thank you for the clarifications. A little later in the article, this is said: "In bilateral prefrontal cortices, the decreased power (“desynchronization”) ranged from alpha (8–13 Hz) to high gamma (50–100 Hz)." Because of this I assumed they were talking about a decrease of power via desynchronization at all times, but that may be innaccurate. This is the only sentence I saw them clarify it as "desychronization", so it could be that it only applies to the bilateral prefrontal cortices.  
> **username_1**: This paper is using that term. They should not, and you shouldn't carry it with you.  
> **username_0**: @BryanKrause So desynchronization doesn't usually lead to a decrease in oscillatory power? Or, something else is usually behind a decrease in oscillatory power?  
> **username_1**: Desynchronization is a possible cause of power decreases in EEG because you can imagine each EEG recording as originating from the sum of many small nodes over some region of the brain near the contact. If those sources are in sync, they will sum. If they are not, some may cancel others out. However, you can also have power changes if individual nodes change amplitude. Separately, desynchronization is also used to refer to the whole broadband EEG, in which "synchronized" refers to brain states in which low frequency power is high (like slow wave sleep) and "desynchronized" is like wake.  
> **username_1**: The authors here may be trying to associate psychedelics with a "more awake than awake" brain state, and they're linking those two types of synchronization in doing so. There are some data that support this general idea, but I don't think that should apply to the data they present in this particular paper.  
> **username_0**: @BryanKrause In response to your third comment: I'm having trouble understanding the last sentence you wrote. So, desynchronization can be used to imply awakeness? Could you elaborate how this meaning arose?  
> **username_1**: The meaning arose because when you are asleep, you have a "slow", synchronized EEG (synchronized in this context meaning lots of slow, low-frequency power). As a bit of an exaggeration, imagine a brain where every neuron oscillates together, from being inactive and hyperpolarized, to a second later being active and depolarized. Slow wave sleep is close to this state. There's very little information in this state, and little information processing if everything is just oscillating together slowly. Wake is very far from this state.  
> **username_0**: @BryanKrause I think I understand: In this second sense, "desynchronization" would be taking a very simple system (a bunch of synchronized, low-frequency neurons), and making it more complex and chaotic. Whereas, in the other sense, desynchronization refers to  the neurons within an ensemble not firing togetherh, and therefore not providing oscillatory power to the band they would usually strenghten. As far as I've understood it, certain ensembles have frequencies they usually abide by, different  parts receiving different types of sensory input, communicate with gamma freq. to bind the info.  
> **username_1**: Yep, that sounds right, up until the gamma binding bit. High gamma activity tends to be correlated with spiking activity, as well as fMRI BOLD signals. I think that's all pretty non-controversial. Besides that, there are many theories. There's a gamma binding hypothesis, which you refer to, though I hear less about that lately. There are theories about gamma being a "feed-forward" and beta (or maybe alpha) being a "feed-back" rhythm, with modest support. Authors of different papers will mention one theory or another but it's all very much under investigation.  
> **username_0**: @BryanKrause Very interesting all of this, thank you for all the information :)  

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## 0 answers

