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Offlinemorrowasted
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Serotonergic psychedelics LSD & psilocybin increase the fractal dimension of cortical brain activity in spatiotemporal domains * 1
    #26981518 - 10/12/20 03:15 PM (8 days, 17 hours ago)

https://www.sciencedirect.com/science/article/pii/S1053811920305358

Quote:



Psychedelic drugs, such as psilocybin and LSD, represent unique tools for researchers investigating the neural origins of consciousness. Currently, the most compelling theories of how psychedelics exert their effects is by increasing the complexity of brain activity and moving the system towards a critical point between order and disorder, creating more dynamic and complex patterns of neural activity. While the concept of criticality is of central importance to this theory, few of the published studies on psychedelics investigate it directly, testing instead related measures such as algorithmic complexity or Shannon entropy. We propose using the fractal dimension of functional activity in the brain as a measure of complexity since findings from physics suggest that as a system organizes towards criticality, it tends to take on a fractal structure. We tested two different measures of fractal dimension, one spatial and one temporal, using fMRI data from volunteers under the influence of both LSD and psilocybin. The first was the fractal dimension of cortical functional connectivity networks and the second was the fractal dimension of BOLD time-series. In addition to the fractal measures, we used a well-established, non-fractal measure of signal complexity and show that they behave similarly. We were able to show that both psychedelic drugs significantly increased the fractal dimension of functional connectivity networks, and that LSD significantly increased the fractal dimension of BOLD signals, with psilocybin showing a non-significant trend in the same direction. With both LSD and psilocybin, we were able to localize changes in the fractal dimension of BOLD signals to brain areas assigned to the dorsal-attenion network. These results show that psychedelic drugs increase the fractal dimension of activity in the brain and we see this as an indicator that the changes in consciousness triggered by psychedelics are associated with evolution towards a critical zone.





Can anyone with a neuroscience background break this down a bit?


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OfflineSugabearcrisp
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Re: Serotonergic psychedelics LSD & psilocybin increase the fractal dimension of cortical brain activity in spatiotemporal do... [Re: morrowasted] * 1
    #26982001 - 10/12/20 07:42 PM (8 days, 13 hours ago)

Really interesting. 

Mathematically fractals are end result of naturally repeating sequences that represent algorithimic growth that happens to describe how life organizes. For the purposes of this article they are using the level of fractilness as a measure of complexity within the otherwise randomness of a brain's neurons.

From wikipedia

Quote:

One way that fractals are different from finite geometric figures is the way in which they scale. Doubling the edge lengths of a polygon multiplies its area by four, which is two (the ratio of the new to the old side length) raised to the power of two (the dimension of the space the polygon resides in). Likewise, if the radius of a sphere is doubled, its volume scales by eight, which is two (the ratio of the new to the old radius) to the power of three (the dimension that the sphere resides in). However, if a fractal's one-dimensional lengths are all doubled, the spatial content of the fractal scales by a power that is not necessarily an integer.[1] This power is called the fractal dimension of the fractal, and it usually





key quote from the study

Quote:

Studies with psilocybin have found that the patterns of functional connectivity in the brain undergo dramatic reorganization, characterized primarily by the rapid emergence and dissolution of unstable communities of interacting brain regions that do not occur in normal waking consciousness...




They describe the brain as a system in which higher levels of activity are increases in entropy, but the real critical piece is the application of fractal measurement to the entropy to separate meaningful increases in activity from just random neuron firing.

Quote:


We stress that entropy is not identical to randomness in all circumstances (it is entirely possible to have a highly structured system with higher entropy), but rather in this context, many of the measures, such as LZC monotonically increase with randomness. This is a useful, but limited understanding of “complexity”, particularly in the context of critical systems, prompting our proposal of fractal dimension as an additional measure that can be related to critical processes






They also discuss criticality as a transition from our normal non plastic hard wired brain to a state of increased plasicity (flexibility) of neurons to connect in novel (new) ways.

The underlying implication is the pyschedelics create increases in brain activity that are analagous to a higher state of function in which new pathways are built and old ones potentially overwritten.


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Offlinesonoramo
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Re: Serotonergic psychedelics LSD & psilocybin increase the fractal dimension of cortical brain activity in spatiotemporal do... [Re: Sugabearcrisp] * 3
    #26983273 - 10/13/20 02:07 PM (7 days, 19 hours ago)

Interesting article. I carried out research developing MRI systems and fMRI sequences. I also carried out (ahem, unsanctioned...) experiments with mushrooms, but not while getting scanned. So it's interesting to imagine what these experiments would be like.

MRI time is expensive, and that probably explains the rather small number of volunteers who got to participate. 20 for the LSD comparison and 14 for the psilocybin comparison. That's a really small group. Presumably these were all experienced psychonauts.

The dosages are moderate, 75ug LSD and 2mg of psilocybin. I have no experience with LSD, but 2mg psilocybin is comparable to 0.4g dried mushrooms if you believe your mushrooms are 0.5 percent actives by dry weight. It didn't say if the volunteers had previous experience with either substance. If I were inexperienced with mushrooms or MRI, even that low dose coming on while inside an MRI system running 15-minute fMRI sequences could be scary. It might also be difficult to remain still for 15 minutes at a time, as is required to get the best MRI data. Since I'm very experienced with both, I'd probably find it interesting. Hell, if I still had access to an MRI machines and a tech to run it for me, I'd do the experiment on the sly. Presumably the volunteers didn't have any claustrophobia issues or fears of being pushed into a machine that makes very loud brrrup-brrrup-brrrup noises for 15 minutes at a time.

I think these are interesting results, especially given the low-ish doses given. It supports the idea that low-dose effects have some physiological reality. Fractal dimensionality corresponds pretty well to what my brain seems to do under the influence of mushrooms. They came up with a creative way to compare spatial fractal dimension with other chaos measures in MRI and MEG data. The tools they used (Python/Numpy/PyEEG and MATLAB) are familiar to me, and I'd love to have at their data, given the chance.

On the other hand, the experiment leaves a lot of questions unanswered. No criticism of the researchers, just a note about how limited their budget was for this experiment. It would have been nice if they could run diffusion-tensor sequences as well as BOLD sequences (which measure localized activity). I bet they would have done this if they had the $$ for it. Diffusion tensor mapping shows the actual connectivity within the brain, and it would be really interesting to see if "subjecting" someone to regular high doses of psychedelics modifies the structural connectivity in the brain. I'd also want to know if how long structural and physiological changes persist. They tested probably over a few hours before and after infusion. But what happens as the volunteer comes back down, and what happens in the days following?

Since these guys are injecting materials anyway, I think it would be really interesting to see if they could assess differences in brain and even retinal response by infusing selectively, for example, with intracarotid or intraocular injection. Maybe that's something for animal "volunteers" rather than humans,...


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OfflineHolybullshit
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Re: Serotonergic psychedelics LSD & psilocybin increase the fractal dimension of cortical brain activity in spatiotemporal do... [Re: sonoramo]
    #26986579 - 10/15/20 09:55 AM (5 days, 23 hours ago)

So eating mushrooms takes you to the "fractal dimension", lol.


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