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  1. chillinwill
    Almost fifty years ago, the beat poet Brion Gysin (1916 - 1986), described a visual hallucination that he experienced while riding a bus:

    ...Had a transcendental storm of colour visions today in the bus going to Marseille. We ran through a long avenue of trees and I closed my eyes against the setting sun. An overwhelming flood of intensely bright patterns in supernatural colours exploded behind my eyelids: a multidimensional kaleidoscope whirling out through space. I was swept out of time. I was in a world of infinite number. The vision stopped abruptly as we left the trees. Was that a vision? What happened to me? (Brion Gysin, 21 December 1958)

    Gysin, a writer and performance artist, though known for his discovery of the cut-up technique, which inspired writers like William S. Burroughs, was also the co-inventor (along with scientist Ian Sommerville) of the Dreamachine, a stroboscopic flicker device designed to be viewed with the eyes closed and produces visual stimuli.

    At the end of his documentation, Gysin asks, "Was that a vision? What happened to me?"


    According to Dominic ffytche of the Institute of Psychiatry in London, and author of 'The Hodology of Hallucinations,' a study recently published in an issue of Cortex, "Fifty years on we are able to answer Gysin's question." Gysin's hallucinations were quite similar to what Jan Purkinje (1787-1869), the father of contemporary neuroscience, experienced as a child.

    "I stand in the bright sunlight with closed eyes and face the sun. Then I move my outstretched, somewhat separated, fingers up and down in front of the eyes, so that they are alternately illuminated and shaded. In addition to the uniform yellow-red that one expects with closed eyes, there appear beautiful regular figures that are initially difficult to define but slowly become clearer. When we continue to move the fingers, the figure becomes more complex and fills the whole visual field. (Purkinje, 1819)

    When Purkinje moved his fingers, he simulated an effect similar to that of Gysin's Dreamachine.

    Because of the brevity and unpredictability of hallucinations, up until now, surprisingly little is known about brain changes that occur during hallucinations—one cannot anticipate when a hallucination will occur. The chances of capturing a hallucination during a brain scanning are small.

    However, it has long been recognized that flashes of light at particular frequencies, like those experience by Gysin and Purkinje, produce hallucinations of intricate patterns and vivid colors. Indeed, these stimulated visual patterns are described as Purkinje patterns. For anyone who's confused out there, the Purkinje patterns ffytche describes in his paper are much more complicated than the stuff everyone sees after a camera flash or when we stare at the sun too long without protective eyewear. They're actually much more than that.

    "They are more complex...entirely unexpected the first time you encounter them. At slow rates of flashing through closed lids you experience exactly what you might expect, a dull red light pulsing with each flash. At the critical frequency the whole thing changes and colours, patterns and forms appear. The Beat poet Brion Gysin's description puts it better than I can."

    Most people have a rough idea of what a hallucination experience might be like, but when it comes to defining a hallucination, that's more difficult. If a hallucination is defined as 'seeing or hearing something that is not actually there,' then dreams and imagery would be considered hallucinations.

    According to ffytche, visual hallucinations, (people do hallucinate with other senses), "are located in the world around us, not in the mind's eye. They are not under our control, in the sense that we cannot bring them on or change them as they occur. They also look real and vivid, although the things one sees may be bizarre and impossible. Purkinje phenomena meet all these criteria and can thus be considered true hallucinations.

    However, Purkinje phenomena are induced by experiment rather than occurring spontaneously as in the Charles Bonnet Syndrome, an eye disease that causes patients to have complex hallucinations. ffytche points out:

    "We are only beginning to understand just how common this Syndrome is, partly because patients have been unwilling to admit their hallucinations for fear of being labeled as having serious mental illness. Charles Bonnet Syndrome patients almost all hallucinate patterns and geometrical forms identical to Purkinje phenomena. Many also see figures, objects and faces, the types of experience we generally associate with hallucinations. The hope is that what we learn from the Purkinje phenomena will also apply to these other hallucination experiences."

    ffytche also adds that "most people will experience Purkinje hallucinations under appropriate conditions of visual stimulation, although their clarity and ease of induction varies from subject to subject. I have only encountered a few subjects who do not seem to have the experiences for reasons I do not fully understand. I assume the visual systems of such 'immune' subjects are wired up in a slightly different way."


    In ffytche's study, he uses a combination of brain imaging methods, harnessing the technique to examine localized changes in brain activity and changes in brain connections during hallucinations. ffytche reviews what we do know about hallucinations and moves the field forward, by introducing a new experimental approach to studying hallucinations as they occur.

    In the study, six male subjects with no history of epilepsy took part in Functional Magnetic Resonance Imaging (fMRI) and Electroencephalography experiments (EEG), which measured the electrical activity produced by the brain as recorded from electrodes placed on the scalp, and were exposed to High intensity repetitive light. The subjects were trained to push a button whether they experienced a hallucination or not and then drew the hallucinations immediately after completion of the fMRI.

    "We also needed to stimulate the visual system without causing hallucinations to be able to determine which aspects of brain activity specifically related to hallucinations and which were just due to stimulation," ffytche says. "This was done in two ways, one controlling for the amount of light in the stimulus and one controlling for the frequency of stimulation. The EEG and fMRI results were examined both from a topological perspective, to identify the cortical regions activated, and a hodological perspective, to identify changes in connections between regions."

    "We observed increases in activity in visual brain regions", says ffytche, "increases in visual connection strength and an alteration in relationship between visual relay and receiving stations, together suggesting that hallucinations were caused by a transient form of 'blindness'".

    The work highlights the need to consider the hallucinating brain from a wider perspective than previously thought. Changes in both localized brain activity and in connections between brain areas occur during hallucinations, raising further questions as to how these changes interact with pre-existing abnormalities in patients susceptible to hallucinations.


    Topological Method

    The brain is a series of specialized regions each performing different functions and is connected by specific nerve cell pathways to form functional networks. In topological methodology, the regions or 'places' of the brain involved in a specific function are revealed by techniques such as functional Magnetic Resonance Imaging (fMRI), a type of specialized MRI scan which measures the haemodynamic response related to neural activity in the brain or spinal cord. fMRI has come to dominate the brain mapping field due to its low invasiveness, lack of radiation exposure, and relatively wide availability.

    Hodological/Hodotopical Method

    ffytche's research implements the Hodology, (also referred to as hodotopic) framework studies, which revisits Alfred Walter Campbell's forgotten 1905 project: to infer function from hodology, the physiology and pathology of cortex and white matter. It includes not only the study of 'places' of the brain, but also, the connections or 'pathways' of the brain. These 'pathways' are revealed by techniques such as diffusion tensor tractography, a procedure to demonstrate the neural tracts. It utilizes special techniques of magnetic resonance imaging (MRI), and computer-based image analysis. The results are presented in two- and three-dimensional images.

    The combined study of both the 'pathways' and the 'places' is what ffytche refers to as the hodotopic approach, 'topos' meaning place and 'hodos' meaning path. In simpler terms, the 'places' of the brain are 'gray matter' and the 'pathways' are 'white matter.' The hodotopic approach studies both gray and white matter, rather than gray alone.

    ffytche explains the benefits of taking a hodological approach to hallucinations and neuroscience:

    "The dual perspective of brain places and pathways helps us remember that the brain is an integrated system and focuses research attention on specific anatomically constrained networks. For hallucinations, we have known something of the cortical 'places' involved for some time and have some idea of how the connections between these 'places' differ in patients with a predisposition to hallucinations. However, we have very little understanding of if, or how, connections change during a hallucination. It is possible that these connection changes are the key to understanding what precipitates a given hallucination episode."

    His study outlines the need for answers and suggests ways in which the questions might be addressed. Although current hodological techniques for studying connections in life are virtual, and do not necessarily reveal real nerve fibers, ffytche points out, "So far the virtual findings are entirely consistent with real anatomy, but we do not yet know how far we can push the technique."

    Better understanding of the connections within the relevant brain networks during hallucinations, whether they get stronger or weaker, may help design new treatments for hallucinations.

    When asked what of his results most surprised him, ffytche replied:

    We expected the brain regions specialised for colour, motion and patterns to be activated during Purkinje phenomena from our previous work. We also suspected there would be changes in connections in visual circuits. What we did not expect was how complex these connection changes seemed to be. Some of the connections changed over time tracking the evolution of Purkinje phenomena. Others were more fixed, changing as soon as visual stimulation started and preceding the onset of Purkinje phenomena. Most surprising of all was the finding that the flashing light stimulus seemed to cut off inputs to the brain, transiently 'blinding' subjects and giving them the experience of what it is like to have Charles Bonnet Syndrome.

    By Jen Palmares Meadows
    Scientific Blogging
    posted: 23 November 2008 10:23 am ET


  1. dyingtomorrow
    This is extremely interesting, thanks for posting it.

    I was wondering the other day: it's so weird how different chemicals can alter our brains and how we think. Why is that? are some of these states superior consciousness? Superior or just different and pointless?
  2. NeuroChi
    The term 'superior' seems very ambiguous in this sense.

    Humans have the opportunity to delve into altered states of mind because they do not directly decrease our chances of survival. Animals in the wild cannot readily eat magic mushrooms or fermented fruit because such substances would inhibit their ability to defend themselves.
  3. Expat98
    Another article about the physiological basis of hallucinations.


    Physics Makes a Toy of the Brain

    Can physics tell us about ourselves?

    To phrase the question more narrowly: can the statistical tools which physicists have developed to understand the collective motion of large agglutinations of particles help us figure out what our brains are doing?

    If Jack Cowan and his colleagues are correct, ideas from statistical physics can tell us important facts about our own brains. By studying the recurring motifs of hallucinations, we can construct a geometry of the mind.


    It's hard to imagine any sort of regularity in a phenomenon as eccentric as visual hallucinations. Our culture is brimming with psychedelia, music and art produced "under the influence" of one or another infamous chemical. Yet the very fact that we can label artwork as "psychedelic" suggests that the effects of those mind-bending substances have a certain predictability. In the 1920s, long before the days of review boards and modern regulations for human experimentation, the neurologist Heinrich Klüwer ingested mescaline and recorded his observations. He reported visual hallucinations of four distinct types, which he called "form constants." These form constants included tunnels and funnels, spirals, honeycomb-like lattices and cobweb patterns. Similar structures have been reported with other drugs, like LSD; these same form constants also appear during migraines, in "hypnogogic" (falling asleep) and "hypnopompic" (waking up) states, when pressure is applied to closed eyes, and even in ancient cave paintings.

    If the same hallucinatory images appear from many causes, might they be indicative of some more general property of brain structure?

    In the late 1970s, Cowan began to suspect that the culprit was not mescaline or LSD itself, but rather the visual cortex at the back of the brain, and in particular the section known as the primary visual cortex, V1. (In technical terms, this means focusing on topological rather than hodological hallucinations, studying those which might arise from a specific part of the brain rather than from malfunctions in the connections among multiple regions.) From magnetic-resonance imaging studies, we know that V1 becomes active when a subject is asked to examine closely an image presented to the eyes. Neuroscientists have discovered a great deal about V1; we know, for example, that its cells are organized into columns, perpendicular to the cortical surface, which are about a millimeter wide (the exact size varies among different mammal species). However, Cowan realized, to a decent first approximation, the visual cortex could be treated mathematically as a uniform surface, essentially a flat plane.


    What patterns of activity would arise when this patch of brain-stuff is perturbed by some outside influence? The answer lies in V1's symmetry: no matter where you stand over it, it looks roughly the same. Shift (or translate) it left or right, and it appears unchanged. To a mathematician, this approximate "translational symmetry" carries a direct implication: the natural patterns or "eigenmodes" of neural activity moving across the cortex will be plane waves.

    Imagine a wave whose crest is a straight line, rippling placidly across a tank of water. The situation in V1 is much the same, except that instead of the displacement of water, the quantity of interest is the neural activity at a given point. In physics jargon, the set of all points and their associated neural firing rates constitutes a field, and the variation over time of that field is tractable via the tools of field theory.

    Oddly enough, this thread of the research stretches back to Alan Turing. After he won the War for England by breaking the Enigma cipher and reading Hitler's mail, Turing grew interested in biology. In particular, he tried to explain how periodic patterns — from the centipede's segments to the zebra's stripes — could arise from the flow of chemicals during embryonic development. Turing described, in the last paper he published, what he called "The chemical basis of morphogenesis": he imagined two substances, an activator and an inhibitor, which spread throughout the developing organism. The activator would, for example, up the production of the pigment melanin, while the inhibitor would decrease it. Turing found that if one chemical spread more rapidly than the other, then the smooth placidity of the uniform expanse of cells could break down, and a pattern of stripes would arise: rows of dark cells with lots of melanin separated by strips of light cells with none.

    Now, clever as this idea was, it isn't the way organisms make segments. The way repeating vertebrae get made, for example, is through a different, but equally seductive mechanism. However, one of the odd things about mathematics is that it can have uses beyond the place where it was first invented. In the study of the brain, we also hear about "activation" and "inhibition": individual nerve cells can be stimulated to greater levels of activity by certain inputs, and reined back by other inputs. Turing's basic scheme for studying how a placid sheet of cells can suffer a breakdown of its stability and see a repeating pattern arise turns out to be just the thing for getting a handle on how patterns of activity can shape themselves in the cortex.


    The relationship between the eyes and the visual cortex is an interesting one, with significant ramifications. It is not the case that, if a square is projected onto the retina, the cortical columns in V1 will "light up" in a square pattern, like the image from a camera being reproduced on a television screen. Instead, a more sophisticated "mapping" exists between our field of view and our primary visual cortex, a relationship known as a complex logarithmic map. A complex logarithm turns circles into straight lines, for example, so that if we stare at a light circle on a dark background, a straight line of neural activity will cut across V1. (If two lines meet at an angle, a complex logarithmic map will turn them into two other lines meeting at the same relative angle. This is a type of conformal map, which preserves angles locally but distorts shapes at larger scales.)


    The logical question is then, what images seen by the eyes correspond to the eigenmodes characteristic of the perturbed V1? What would you have to see for the ordinary activity of V1 to look like the patterns seen when the brain is perturbed by a migraine or a drug?

    The answer is that the eigenmodes of this simple model correspond to two of Klüver's form constants.

    Now, the visual cortex is not a perfectly uniform, completely symmetric surface. For starters, the cortex can recognize orientation: patches of cortex have a sense of directionality, such that a particular small piece of cortex will become active when its region of the visual field contains a feature tilted at a certain angle. (In the macaque, for example, these "iso-orientation patches" are about 0.7 mm across, the width of a mechanical pencil point.) When this feature is added to the cortex model, the other two form constants emerge from the equations. Shapes seen in hallucinations arise naturally from the symmetries of V1.


    I had the good fortune to see Jack Cowan explain this research in person, although on that day, the emphasis was on other ways the model could be tested — using EEG measurements and so forth — rather than on hallucinations provoked by the 1960s. For that, the reader can watch the video from California.

    A complex-systems expert who sat next to me in the audience opined that Cowan had "averaged out the neuroscience" in the first few minutes of his presentation: this model of the cortex omits almost all of the detailed biochemical knowledge we have on neurons. This is at once the blessing and the bane of such research.

    Physicists like to joke that their field studies "spherical cows", entities so far abstracted from the real world that they lose the relevant details. Studying vast collections of neurons using statistical field theory is rather like dissecting the brain of a spherical cow: If a "toy model" exhibits behaviour which resembles that of the real, living system, then we can provisionally neglect the intricacies of detail. Features in EEG traces or visual hallucinations which occur on top of the toy model's predictions might then be due to those biological peculiarities.


    Those who wish to brave the mathematical details can read the literature:

    * P. C. Bresloff et al., "What Geometric Visual Hallucinations Tell Us about the Visual Cortex" Neural Computation 14 (2002):473–491. Also available here.

    * M. Buice and J. Cowan, "Field-theoretic approach to fluctuation effects in neural networks" Physical Review E. (29 May 2007).

    For a broader perspective, try the review article

    * G. Deco et al., "The Dynamic Brain: From Spiking Neurons to Neural Masses and Cortical Fields" PLoS Computational Biology 4, 8 (2008).

    This is very much a field under development. To get the flavour of current research, see, e.g., the preliminary report of Daniel Fraiman et al., "Ising-like dynamics in large-scale functional brain networks" (2008), arXiv:0811.3721.


    November 27, 2008

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