Concert cellist, Katinka Kleijn, can play a duet with her own brain.
"It was really interesting when I heard the sound of my own brain — or a translation of my own brain waves into sound," she says in the audio file below, which we first saw on Buzzfeed.
Kleijn achieves such a feat by wearing an electroencephalography (EEG) headset, her composer Daniel Dehaan tells Business Insider. Billions of small cells called neurons compose the human brain. They communicate with each other by emitting electrochemical impulses, which the headset can measure.
"It reads these electrical impulses between neurons and the brain ... which aren't actually sound themselves but just signals," he says.
Dehaan then uses a program called Max/MSP to translate those signals into audio. Initially, they appear as data, which he must scale as directly as possible into values appropriate for sound. He doesn't assign brain waves instrumental sounds, like a clarinet or a drum. Instead, they create an entirely unique sound.
"We receive many separate streams of numbers [from the headset] ranging from very small increments to very large," Dehaan explains. Initially, the company who made the headsets wouldn't provide a key, a huge challenge the team.
Another problem arises when translating the data too — most of the brain's electrical impulses occur at frequencies below what the human ear can hear. The brain exchanges electrical impulses at about 0 to 30 hertz, while human hearing ranges from 20 to 20,000 hertz. For some perspective, the cello has a frequency range of about 65 to 880 hertz.
That means the human ear simply can't hear certain sounds. "You might feel a vibration in your stomach or your chest though," Dehaan says.
The frequency of brain waves also reveals information about the person's psychical and emotional state. For example, increased activity in the 8 to 13 hertz can suggest someone feels relaxed but aware, while anywhere above that implies alertness, agitation, tenseness, or fear. Colored spotlights during Kleijn's performances also indicate the strengths of her four affective states: meditation (blue), engagement (green), excitement (yellow), and frustration (red).
Believe it or not, Kleijn has a much more difficult job than Dehaan. During a performance, she must play the cello and simultaneously react to words, like "grief" or "excitement" that flash across a screen in front of her along with small musical fragments. She controls when the words or fragments appear with two foot pedals while she plays.
"I can't do what she does," Dehaan says.
To start the rehearsal process, Kleijn needed to become accustomed to the sound of her own brain and learn to control it. Easier said than done.
If the word "calm" flashed across the screen, the second Katinka would feel calm, she'd become excited about feeling calm, which would change the sound, Dehaan tells Business Insider. Then, she'd immediately become frustrated she lost the feeling of calmness, changing the sound once again.
"You're constantly aware of your own emotions," he says. "And it's amplified because everyone else in the room also is."
Watch the full video of her performance at the Chicago Cultural Center in 2013.
"Did she [Kleijn] have a lot of coffee this morning? Did she have a good conversation with the last person she spoke with?" Dehaan inquires. "It opens up this inner world of the performer while she performs." The audience hears the evolution of Kleijn's brain's response to stimuli.
Exploring this technology and its relationship to the brain has potential far beyond music, as well. Dehaan remembers one concert in Chicago where a woman told him that she used a similar EEG headset of her mentally disabled son to help him understand and develop his learning strategies.
"The applications are endless," Dehaan says.