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Comment by GuiA | Hacker News Reader

This idea of reality being "passed through" multiple filters, and these filters being reduced or disabled on psychedelics, is developed (somewhat unscientifically) by Huxley in "The Doors of Perception"- it's a fairly good read.

If I remember correctly, the main criticism against this is that if it were the case brain activity should be reduced, at least in some regions, when on psychedelics. However, observing people on psychedelics with fMRIs does not match with that.

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However, observing people on psychedelics with fMRIs does not match with that.

This study would appear to disagree: http://www.pnas.org/content/109/6/2138

Decreased activity in the ACC/medial prefrontal cortex (mPFC) was a consistent finding and the magnitude of this decrease predicted the intensity of the subjective effects. Based on these results, a seed-based pharmaco-physiological interaction/functional connectivity analysis was performed using a medial prefrontal seed. Psilocybin caused a significant decrease in the positive coupling between the mPFC and PCC. These results strongly imply that the subjective effects of psychedelic drugs are caused by decreased activity and connectivity in the brain's key connector hubs, enabling a state of unconstrained cognition.

If you have bottom-up sensory associations and top-down inhibitory control (the filters), only inhibitory signals would be reduced. You would actually see more brain activity, since the bottom-up sensory associations would be less inhibited, and therefore trigger a greater amount of neurons. Probably an over-simplification, but you can see how it would be tough to use an fMRI to measure reduced inhibition and increased activation.

maybe the mechanism of "shutting down" these processors is not about ON/OFF behaviour, bur rather just disconnect from processing pipeline, not being in sync with other ongoing processes etc.

generally brain on psychdelics is in "overdrive" mode (confirming on myself), but maybe not everything is on turbo in same way, and works seamlessly in normal state doesn't work well anymore

Why would it follow that less filters would infer less brain activity? - even partially. Surley any cleansing/removing of the filters would excite all the brain, as it reacts to new stimuli.

To quote Huxley "If the doors of perception were cleansed every thing would appear to man as it is, infinite. For man has closed himself up, till he sees all things thro' narrow chinks of his cavern."

> Surley any cleansing/removing of the filters would excite all the brain, as it reacts to new stimuli.

"Filter" in this case is just an analogy, and not necessarily a good one. We don't know the nature of consciousness and how it maps to brain activity, so it's not appropriate to assume that what is perceived as removing a "filter" is increasing stimuli, it's just processing it differently in some way.

I was replying to the someone, who it seems has misunderstood what Huxley meant by filters - I wasn't defending or affirming them, let alone discussing in what context they are 'appropriate'. I used the quote to give the 'filters' being discussed a context. Are you saying Huxley really meant: If the doors of perception were cleansed everything would not appear infinite but just 'processed differently'?

That's interesting. Could that be because those filters are imaginary in nature?

After all, no specific brain activity can be detected on a person imagining Santa Claus to be real either.

Brain activity is not a precise meassure, not in terms of fMRI, which just shows an increased blood flow.

The hypothesis is obvious on the other hand. However, individuals that would submit to a test on psychedelics is likely the type that gets easily exited just for the sake of it and doesn't. Or brain activity doesn't corralate with actually functioning correctly. I' expect a failing subsystem would respond with increased activity, simple feedback. Eventually some controle unit would shut it off or the subsystem would keep working but a bit unusual, despite increased blood flow.

did the easily exited type bit strike a feeling or why the downvote? I mean, it can't be given to an unsuspecting control group. That would probably feel moderately icky and the desire to rest.

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