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.

Brion Gysin and William S. Burroughs experiencing the Dreamachine

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.

Johannes Purkinje

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.

Examples of patterns induced in different subjects drawn immediately after fMRI experiments.
CREDIT: ffytche Hodology of Hallucinations in Cortex, September 2008

“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.

Hodotopic changes during Purkinje hallucinations. Framework has been extended to include the eye and thalmic relays (LGN and Pulvinar) CREDIT: ffytche Hodology of Hallucinations in Cortex, September 2008

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.
Go here if you'd like to learn more about Brion Gysin's Dreamachine.

Source: Dominic H. ffytche, The hodology of hallucinations, Cortex (2008), doi:10.1016/j.cortex.2008.04.005.