Eavesdropping on the brain can be relatively simple. Scientists just place small metal discs, against the scalp. These electrodes can listen to the brain’s electrical activity. But the signals may appear weak when the electrodes can’t get close enough to the scalp. This may happen when people have coarse, curly hair.
And the result could affect research findings, notes Pulkit Grover. He is an engineer at Carnegie Mellon University in Pittsburgh, Penn. To get around this, some studies simply exclude people with coarse, curly hair. But the issue also can affect what medical tests learn, he says. That’s especially true for EEGs. That’s short for electroencephalograms (Ee-LEK-troh-en-SEF-uh-loh-gramz). These tests can detect changes or problems in the brain’s electrical activity. For instance, EEGs can identify abnormal brainwaves seen in people with certain disorders.
Such tests rely on arrays of scalp electrodes listening in on the brain’s electrical activity. Where the electrodes can’t “hear” well, accurate diagnoses can be hard to make. “It’s not intentional. But at the same time, it’s kind of sad,” Grover says. “It’s worth thinking about technology, and about who it has been designed for.”
Arnelle Etienne did just that. She joined Grover’s laboratory as a college student. She combed through the scientific research on EEG technology. “I noticed that a lot of the current solutions wouldn’t work for my hair type,” says Etienne, who is Black.
Researchers using EEGs, she found, often try to “MacGyver” their way through with tricks to try and make the tests work. Sometimes they would ask patients to straighten their hair before the tests, Etienne learned. But such workarounds wouldn’t always work. That was especially true where EEG measurements were needed quickly. Then the requests are more dramatic. “Some people have been asked to shave parts of their hair to do the test,” Etienne says. “Luckily, that’s not as frequent. But it was shocking to hear.”
A team including Grover, Etienne and another college student, Tarana Laroia, measured how much coarse, curly hair might interfere with measuring brain signals. They found that standard electrodes placed on loose, curly hair created very high impedance (Im-PEE-dunce). That’s a measure of the resistance that an electrical current faces. A good EEG signal should have less than 50 kilo-Ohms of impedance. Unbraided, curly hair with standard electrodes could register 615 kilo-Ohms!
The researchers wanted to get connections closer to the scalp. So they had people braid the study participants’ hair. The braiders created tight, thin cornrows that left the scalp exposed in strategic spots. Along with the braids, the researchers developed flexible electrode clips. The clips are shaped like dragonfly wings. They can be pushed under braids that are nearby. Etienne (whose father is Haitian) and her colleagues call the electrode “sevo.” That is the Haitian-Creole word for “brain.”
Braids anchor the new clips to the scalp. Now the attached electrodes, which sit between the braids, are closer to the scalp, too. And there, they resulted in impedance measurements of 22.6 kilo-Ohms. That’s well within the range for a reliable EEG measurement. The team tested its new sevo electrodes on eight participants and reported their results February 27 at BioRxiv.org.
The electrode problem “doesn’t require the deepest, most amazing science to get a solution,” Grover says. “It requires a good integration with the culture and the understanding of the clinical environment.”