| Seeing colour in the concrete

Studies investigating the cause of hallucinations have established over the years that these originate in the brain’s visual cortex, causing images that, according to a recent article by neuroscientist Paul Bressloff, “are seen in both eyes and move with [the individual].”

A study published in the journal Neural Computation in 2002 examined geometric visual hallucinations, attributing these to a number of causes: “taking hallucinogens such as LSD, cannabis, mescaline, or psilocybin;…viewing bright flickering lights; on waking up or falling asleep;…‘near death’ experiences; and… many other syndromes.”

The study goes on to categorize the types of hallucinations into four groups called “form constants: tunnels and funnels, spirals, lattices (which include honeycombs and funnels), and cobwebs.”  Essentially, these are different geometric patterns.

Physicist Nigel Goldenfeld extended this examination in a similar study last year that engaged with the mechanisms that take place in a brain as it hallucinates. His lab analyzed hallucinations with reference to the Turing mechanism, which plays a part in pattern creation in many biological and ecological systems.

Turing patterns work through a reaction-diffusion system that contain “activators” and “inhibitors.” Through a feedback mechanism, the activating chemical amplifies its own quantity, while an inhibitor keeps it in check by slowing down its production and diffusing it.

“In principle, the behaviour is generic. The trick is that you have to have the right rates for the chemical reactions, the right diffusion rates of reacting species,” Irving Epstein, a Brandeis University chemist who studies pattern formation, told Wired Science. Within the human brain, the visual cortex controls the process of image creation; as light perceived by the eye stimulates certain parts of the visual cortex, a pattern of neural connections form, resulting in an image. Yet these patterns can also arise spontaneously causing geometric hallucinations.

Goldenfeld and his research team posit that the topological structure of the visual cortex inhibits Turing patterns from working over long distances, and from producing spontaneous neural connections consistently.

This means that while certain changes in the ‘normal’ workings of the visual cortex may cause geometric hallucinations, the patterns caused by external stimuli will still be those most predominantly seen – at least in the average human brain.

Yet individuals who have no cognitive or psychological illnesses often report encountering minimal hallucinations within the course of their daily lives, without determining the “form constants” that are responsible for these. Often, the triggers are attributed to altered levels of stress, sleep patterns, or changes in alcohol and/or drug use.

I talked to Michael D’Alimonte, a student at McGill who falls within this subgroup, about his experiences with such hallucinatory occurrences. “The mildest form [of these] would be in terms of set patterns, especially pavement and brick patterns,” he said, “Often, images will swirl, set lines will become fluid. This could stem from staring at something for too long, or being in an environment with many patterns… I can easily stare at a set of lines or a brick wall for it to morph and start moving.” Often he finds that staring at concrete causes it to move.

For D’Alimonte, the hallucinations accord with the categories found in the aforementioned study. “It may be more of a honeycomb kind of thing, it’s so spread out and varied that it eventually just becomes one big kind of mesh. I guess the speckles in the concrete stop being confined in place and just become everywhere.”

A variation that also accords with the study, and may be linked to sleep paralysis, is found with hallucinations that occur upon waking up or falling asleep.

“There’s a strange kind of state between sleeping and consciousness where my mind will be awake, but my body isn’t fully awake yet,” said D’alimonte. “My eyes will be open, my mind will be at work but my body won’t be able to move. The most recent case was when I was napping on my couch and my mind woke up but my body wasn’t awake yet, and on the chair next to me was a fully formed person… just chilling on my couch watching TV with me, which at the time freaked me out. Once I calmed my mind down enough to fully wake up, this person was not there anymore. That’s one of the key instances which I don’t know if you can classify as dreaming… you know when you’re dreaming because your body will respond to you… I knew I was awake, my body wasn’t working and I saw things I didn’t see when I was actually conscious.”

Neurologist and author Oliver Sacks has engaged with yet another aspect of hallucinations among psychologically healthy individuals with visual impairments, called Charles Bonnett syndrome, in a TEDTalk.

His studies have determined that over the course of a person’s life, there are subtle changes that can occur within the structural set up of the visual cortex, causing one to hallucinate. “There is a special form of hallucinations that could go along with deteriorating vision or blindness… As the visual parts of the brain are no longer getting any input, they become hyperactive…they begin to fire spontaneously and you start to see things,” said Sacks in his TEDTalk.

Speaking about one of his patients who experienced these, Sacks states that “she was perfectly sane, she had no medical problems, she wasn’t on any medications that could produce hallucinations… The hallucinations were unrelated to anything she was thinking, feeling or doing. They seemed to come on by themselves or disappear. She had no control over them…they all seemed oblivious to her.”

It appears, then, that subtle variations within the visual cortex are capable of inciting perceptual changes within the largely healthy human brain. With the human tendency for nuanced individual differences, perhaps it is not so easy to compartmentalize variations from the ‘average’ visual perception.