Imagine eating a certain food and "tasting" a colour. Or seeing an object that elicits a particular smell. Or hearing a particular piece of music and feeling as if you are physically flying in concert with the sound.
Such simultaneous sense experiences are an everyday reality for people born with synesthesia. But for a Toronto man, the intriguing neurological condition developed months after he suffered a stroke – and it has changed the way he sees the world.
George, who asked that his real name not be used, is believed to be only the second person worldwide to have acquired synesthesia as a result of brain damage, say neurologists at Toronto's St. Michael's Hospital involved in his case.
The other was an American, whose stroke also damaged the part of the brain known as the thalamus. But George is the first reported case of acquired synesthesia manifesting itself in multiple senses, and he's also unique in that he can stop the sensations at will.
For George, the first inkling that something had dramatically changed after his 2007 stroke occurred while he was watching a performance of the Peking Opera at the opening ceremonies of the Beijing Summer Olympics. The high, siren-like voices of the women triggered an unimagined response.
"I didn't just hear the music, but I could feel it going through me," the 40-something patient recalled Tuesday. "Then I could see the music and then I felt that – and this is so weird – I felt that I was being pulled into the TV set, travelling through the air magically and winding up in Beijing.
"It was absolutely wonderful ... I was floating above the crowd and I could feel the heat and humidity off the crowd, and the smells. It was like being at the Olympics. I went from an air-conditioned condo to being up on the 50th row of the Olympic stadium."
Some of the experiences that followed were not so pleasant: he went into a grocery store and saw a sign advertising chicken. The letters were a powder blue and the colour set off an emotional response he couldn't explain.
"All I could do was stare at the light blue colour and it was making me angry. And I felt disgusted. And then I started to think the chicken might be dirty," said George, who felt nauseated at the sight.
He also developed a craving for raspberries, which he'd never had much interest in before. While eating the fruit, he would see a light blue halo in the periphery of his left eye. And while they tasted like raspberries, they also "tasted blue."
"I also taste blue inside my mouth," he said, trying to put into words an experience most of us would struggle to comprehend. "I taste what it looks like."
His sense of smell can also be triggered. One night in bed, the feel of the sheets on his leg brought forth an odour he related to a painting he'd seen by Cornelius Krieghoff – not the odour of an oily, musty canvas, but "it smelled the way the painting looks."
George, who works in the performing arts, discovered that the sound of certain musical instruments can also bring on synesthesia.
High-pitched brass instruments – such as those played in the James Bond movie theme – create a sense of euphoria.
"I could ride the music, that's what I call it," he said. "It's like flying through space at the speed of light on top of ribbons of sound."
Tom Schweizer, director of the neuroscience research program at St. Mike's, said George's stroke occurred in the thalamus, a walnut-sized structure in the middle of the brain that connects dense bundles of nerve fibres to different parts of the brain, acting as a sort of hub or central relay station.
The neurologist said the brain is "brilliant at trying to fix itself" after being damaged by a stroke or head trauma. The phenomenon, known as neuroplasticity, can mean the creation of new connections as the brain tries to return to normal function.
Because the damage was in the thalamus, it may be that the complex job of rewiring in George's brain went somewhat awry, Schweizer said.
"And now areas that would never be in direct communication with one another are speaking to one another and are getting fired or getting online from different types of stimuli."
Schweizer and a team of neurology colleagues decided to look for physical proof of George's synesthesia. They imaged his brain using functional MRI while playing the James Bond theme "and it lit up all over the place," he said.
They also put six healthy volunteers of the same age and education through the same test – and as expected, only their brains' auditory cortex was activated by the music.
A report on George's case was published recently in the journal Neurology. The researchers plan further study of George, who has not only become a synesthete, but has also developed an acute autobiographical memory he did not possess before and a strong sense of deja vu.
Those neurological traits are not related to synesthesia, either acquired or the developmental form that affects an estimated one per cent or less of the population. Those born with the condition include singer-songwriter Billy Joel, composer Franz Liszt and author Vladimir Nabakov.
People born with synesthesia are powerless to stop the mix of sensual responses that confronts them, which is often related to seeing a certain colour. For example, a synesthete might always see the word "juice" as red or the letter "w" as green or the number 9 as purple.
George, however, is able to suppress, or mentally turn off his synesthesia if the sensual overload is too distracting.
"If I couldn't control it, this would be hellish," he said. "If I'm driving up the Don Valley Parkway (in Toronto) and I start to have a synesthesia, I'm just like, 'I've got no time for this right now, I'm driving a car."' Dr. Luis Fornazarri, the behavioural neurologist who first treated George at St. Mike's, said many people with synesthesia hide the condition because they think they are "weird."
But it is not a disease and there is nothing wrong with their brains, he said. "I think they are privileged because they can see and experience sounds and experience taste and so on."
At first, George also thought he was going crazy, but now he embraces his synesthesia.
"I hate having the stroke, and my arm doesn't work very well. I still have numbness on my right side to some extent," he said.
"But if I had to give up the synesthesia in order to get better, I would not take the offer.
"I got something really great in return."