How Geometric Hallucinations Are Generated in the Brain

geometric hallucinations

This article is based on a lecture delivered by Professor Jack Cowan at an event entitled ‘A Discussion on Scientific Research with Psychedelic Drugs’ (the conference was chaired by Professor David Nutt at Imperial College London, 12/06/2013).

There are many causes of geometric hallucinations, including:

  • Flickering lights (a phenomenon which the scientist Jan Evangelista Purkinje investigated)
  • Anaesthesia
  • Hypnagogia (For more about this see my other article)
  • Near-death experiences
  • Entoptic phenomena (these are visual effects whose source is within the eye or brain  itself – you can see entoptic phenomena when you press into your eyes…although don’t do it too hard!)
  • Psychoactive drugs
  • Various conditions such as migraine and epilepsy
  • Sensory deprivation

Professor Jack Cowan says that two of the most inspiring intellectuals he has studied have been Claude Shannon (known as the “father of information theory”) and Alan Turing (known as the father of computer science and artificial intelligence). One paper which influenced Cowan’s model of how geometric hallucinations occur is his Turing’s 1952 paper, The Chemical Basis of Morphogenesis. In this paper, he shows how the stripes on a tiger and the spots on a leopard can naturally occur. These patterns are the result of the interaction of two chemicals that spread throughout a system, like how a gas spreads throughout a box. The difference, however, is that the chemicals, which Turing calls morphogens, spread at different rates. One can be seen as the activator which expresses a particular quality (e.g. a blob or a stripe) and the other can be seen as an inhibitor (preventing the particular quality from being expressed).

Whether this explanation for patterns in nature is valid remains to be seen. Some say it is a bit too simplistic. In any case, Cowan argues that this Turing mechanism of diffusion and inhibition can be used to explain how visual geometric hallucinations result from brain activity. If neurons can be described mathematically in terms of “activators” and “inhibitors”, then that could explain why we see recurring patterns when we hallucinate.

Cowan believes that we should keep R. Mourgue’s (1932) words in mind: “The hallucination…is not a static process but a dynamic process, the instability of which reflects an instability in its condition of origin.”

The random fluctuations in brain activity might technically be “noise”, but even if it is, the brain still manages to transform it into a pattern. But how? Cowan says it’s all to do with the physical structure of the brain. With eyes closed, since there is no external input, the geometric hallucination should reflect the architecture of the brain; more specifically, the architecture of the visual cortex. The brain can generate geometric hallucinations out of an unstable state because the architecture of the primary visual cortex (V1) exhibits symmetry (see diagram below). There is evidence that the orientation columns (which display a shift-twist symmetry) and the interconnected modules or hypercolumns (which display a lattice symmetry) can create geometric hallucinations when appropriately stimulated.

The architecture of the brain is also fractal by nature – the same patterns are repeated at different scales of size. This could, therefore, explain why fractal hallucinations are reported by those who take psychedelic drugs. Medical researcher Robin Carhart-Harris has commented on this, saying: “Like tree branches, the brain recapitulates. You are not seeing the cells themselves, but the way they’re organised – as if the brain is revealing itself to itself.” So, if you ever start hallucinating fractal geometry, that means you’re getting a good look at how your brain is structured.

Professor Cowan goes on to discuss cave art and how some of the geometric patterns drawn on the cave walls are signs of hallucinations. He refers to the work of archaeologist David Lewis-Williams who, in his book The Mind in the Cave, argues that the blob, dot and lattice patterns in the Chauvet cave are hallucinatory in nature. He argues that the hallucinations could have been the result of being in a dark cave with a flickering light, such as a fire. It has already been established by scientists, such as Purkinje, that a flickering light is capable of producing geometric hallucinations.

Cowan then goes on to discuss entoptic forms (Tyler, 1978) which are the basic visual patterns that come from the eye or brain itself. Lewis-Williams claims that entoptic forms can be found in San Bushmen rock art and Paleolithic rock art. Funnel and spiral images generated by LSD were studied by Oster (1970), whose study was based on his own experiences, and by Siegel (1977), whose study was based on the experiences of his subjects. The images they produced were extremely similar, suggesting that the geometric hallucinations generated by LSD are universal, and can, therefore, be attributed to an identifiable process in the brain. Just as Carhart-Harris has argued, hallucinating geometry is the experience of seeing the structure of your brain.

Heinrich Kluver, in Mechanisms of Hallucination (1942), organised entoptic forms into 4 classes which he called form constants. According to Kluver, all geometric hallucinations should fit into one of these categories. They are (1) Tunnels and funnels, (2) Spirals, (3) Lattices, honeycombs and checkerboards, and (4) Cobwebs.

A 1959 research paper by David Hubel and Torsten Wiesel found that there were neurons specialised for the detection of lines, orientation, corners and edges in the brains of cats. The famous neurologist and psychiatrist Oliver Sacks suggests in his book, Hallucinations (2012), that if these neurons in humans are stimulated by a psychedelic drug, geometric hallucinations can be generated.

Further reading


  1. Anonymous
    June 23, 2013 / 9:53 am

    Hey Sam, I quite liked this post. The subject is interesting and your approach intriguing. Would you happen to have full citations of the sources mentioned in the text? Thanks in advance. Keep writing. Love.

    • June 23, 2013 / 4:16 pm

      Glad you enjoyed it. I don't have the full citations myself – the post is essentially just my typed up notes from the lecture by Professor Cowan, plus some more information I came across.

    • June 23, 2013 / 9:14 pm

      I just added a link to one of the papers that Jack Cowan co-authored – you will find the full citations there.

    • Anonymous
      June 23, 2013 / 9:56 pm

      Great article, I'm glad that there is finally some serious research being done about these phenomenon, I feel that it will reveal much about how our brains work and the fractal nature of reality.
      I've been also very interested in why certain fractal motifs are associated with different substances. Such as; melting with LSD, aztec style motifs with psilocybin, and persian mandalas with syrian rue, etc. Are these dictated from the chemical compounds themselves or could we possibly be tapping in to some sort of repository of previous experience?

    • June 24, 2013 / 6:57 am

      My personal opinion is that what these drugs do is tap into the unconscious. The stronger the experience means the more you have tapped into a hidden, inner realm, and the less you have tapped into the known, outer world. That's interesting you associate different imagery with each drug – I've definitely heard aztec motifs reported with psilocybin. I've also heard that DMT can produce imagery from every culture (Arab, Indian, Aztec, Native American, Egyptian, African etc.) It makes you wonder how much of a culture's art is influenced by these experiences…

    • Anonymous
      June 24, 2013 / 6:40 pm

      Clearly the culture is influenced by these experiences and vice versa. It makes sense that DMT can produce motifs from all cultures since it's produced by our brains and also found in thousands of plants around the world. But I have been intrigued specifically buy various ayahuasca brews where I see the MAOI as an interpreter of the DMT, from my experience in brews using Syrian Rue as the MAOI I've seen a lot more persian and oriental patterns as opposed to a brew with Banisteriopsis caapi where I'd experience much more shipibo and south american style visuals even while using the same plant source for the DMT. Of couse some imagery and experiences transcend all cultural motifs.

      Although I personally see the mind as a microcosm of the universe in that the difference between "going deep inside the mind" and "travelling to other worlds" is arbitrary. It's all just different levels of the same fractal. But my question is if you are just going into your mind how would you experience motifs from cultures that are not part of your DNA? Also what about all the shared experiences that many have reported? Do you believe in non-local consciousness?

    • June 24, 2013 / 7:54 pm

      I'm not sure why we experience these motifs – it could be a combination of archetypes (which are a part of our psychology), memories, hallucinations (which we interpret as 'Aztec' or 'Egyptian' based on their similarity to art we have seen). As you say, different drugs (and different drug combinations) often give distinct imagery – that could just result from the drug (or drugs) interacting in a certain way with our mind. Who knows – it's a still a mystery to me.

      I don't believe in non-local consciousness, no. I think that the brain produces consciousness, or that consciousness emerges from the brain.

  2. Anonymous
    July 2, 2015 / 4:41 am

    I've gotten these fractal patterns for years just before falling asleep – with no drugs involved, and always thought it was quite a weird phenomenon. Usually I have to be sleep deprived or it won't work. I see geometric shapes moving about (with my eyes closed) pinwheel-like objects twirling, etc. It is amazing to me that my mind can create these perfect shapes out of nothing for no real reason since I don't take drugs. (I don't suffer from epilepsy, psychosis, or anything of that nature. Age 63, m.) Sometimes I find it entertaining watching these shapes move about, as I'm about to nod off. I always wrote it off as a brain chemical caused by sleep deprivation, because it doesn't happen unless I'm really tired.

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