A New Theory of Psychosis?

By Neuroskeptic | October 13, 2012 9:56 am

A team of British neuroscientists led by the (in)famous David Nutt says that magic mushrooms offer a new theory of psychosis: Functional Connectivity Measures After Psilocybin Inform a Novel Hypothesis of Early Psychosis

It’s a reanalysis of a study from earlier this year, which got quite a lot of attention, in which 15 volunteers were injected with psilocybin – the major active hallucinogenic ingredient in ‘magic mushrooms’ – during an fMRI scan.

In a nutshell, the rather interesting proposal in the new paper is that psilocybin may cause mind-altering effects by blurring the difference between the brain networks responsible for ‘internal’ and ‘external’ thought.

Activity in the internal “default mode network” (DMN) is generally anti-correlated with the “task-positive network” (TPN) – when one is higher, the other’s lower. The DMN is active when you’re not doing much – hence ‘default’ while the TPN comes online when you’re engaged in a particular mental activity.

Nutt’s team say, however, that their functional connectivity fMRI data show that after psilocybin, activity in these two networks becomes positively correlated – an unusual pattern. They write:

Increased DMN-TPN coupling has been found in people at high risk of psychosis and an inability to distinguish between one’s internal world and the external environment, sometimes referred to as “disturbed ego boundaries,” is a hallmark of early psychoses and the psychedelic state.

One of our volunteers reported the following after psilocybin: “It was quite difficult at times to know where I ended and where I melted into everything around me.”

To be honest I’d need to see a replication before I put too much faith in this, because this kind of post-hoc reanalysis of fMRI data is very flexible and therefore prone to false positives, but it’s an interesting idea, and at least it provides a clear theory for further research.

ResearchBlogging.orgCarhart-Harris RL, Leech R, Erritzoe D, Williams TM, Stone JM, Evans J, Sharp DJ, Feilding A, Wise RG, and Nutt DJ (2012). Functional Connectivity Measures After Psilocybin Inform a Novel Hypothesis of Early Psychosis. Schizophrenia bulletin PMID: 23044373

  • http://petrossa.me/ petrossa.me

    i dropped lsd for quite a few years, which according to this theory should resemble psychotic state.

    At all times i was fully aware of boundaries, whilst still riding my bike to beautiful church music (the exhaust i knew) upwards in a multicoloured sky.

    I was fully aware i wasn't actually going up but that it was a bad interpretation of the eyes perspective.

    I was on my way to where i wanted to be, and got there.

    It was hard to judge distance though.

    Many other anecdotes.

    My many friends never had issues differentiating between the altered state and reality except those few who went into a bad trip.

    The theory needs many other psychedelics to try before it could even be advanced as one.

  • Ivana Fulli MD

    Neuroskeptic,

    You meant a new hypothesis about psilocybin induced psychosis in a very noisy and”unspiritualfriendly” environement. Didn't you ?

    PS: I never ever treated anybody with it but I would advise psilocybin in the hands of warm and experienced health teams rather than ketamine -after reading the litterature available to poor I (lots of paywalls between I and knowledge since 2008).

  • http://www.blogger.com/profile/06647064768789308157 Neuroskeptic

    A commenter who had trouble with the spam filter emailed me to say:

    “This is not a new theory. In the 1980s memory researchers published several studies suggesting positive symptom schizophrenics had difficulty distinguishing between internal and external events. The typical paradigm involved the visual presentation of single concrete nouns with the instruction to (either) say the word outloud (an external event) or to think the word to yourself (an internal event). Later the subjects were presented with the target words and foils, and expected to report whether they recognized the word, and if so, whether the word had been said (an external event) or thought (an internal event). Positive symptom schizophrenics typically recognized fewer items, and had a definite bias to reporting the items had been said. Normal control subjects were actually biased to reporting the item had been thought. Although there are lots of problems (including whether schizophrenics confound things by subvocalizing), one conclusion is that when the origin of an experience is in doubt, schizophrenics tend to believe the experience was external or real, whereas the rest of use tend to assume the uncertain experience was internal and “just something I imagined…”

  • http://unrelatedpotential.wordpress.com/ unrelatedpotential

    Corollary discharge and efference copy (wiki for a quick overview: http://en.wikipedia.org/wiki/Efference_copy) were proposed as a mechanism for internal/external distinction. Simply put, whenever you, for example, say something, a copy of a “speech command” would be sent to auditory cortex, allowing the brain to recognise this event as internally generated, rather then externally.
    There are some papers on the possible dysfunction of these mechanisms in SZ, like this one: http://www.ncbi.nlm.nih.gov/pubmed/14988645 , though I think there's some discussion on that…

  • pfk

    This (on an abstract level) closely reminds me of every lsd trip I ever had. And also of this neuroscientist's self report of stroke which temporarily disabled some left-hemisphere functions (vivd report of not being able to tell where she ends and everything else starts):

    http://www.ted.com/talks/jill_bolte_taylor_s_powerful_stroke_of_insight.html

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No brain. No gain.

About Neuroskeptic

Neuroskeptic is a British neuroscientist who takes a skeptical look at his own field, and beyond. His blog offers a look at the latest developments in neuroscience, psychiatry and psychology through a critical lens.

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