New electrodes can better capture brain waves of people with natural hair

Snugged up against the scalp, electrodes can eavesdrop on the brain’s electrical activity. But the signals can weaken when electrodes can’t get close enough to the scalps of people with coarse, curly hair. 

This design flaw could end up excluding people with this type of hair, including people of African descent, from studies, says engineer Pulkit Grover of Carnegie Mellon University in Pittsburgh. The issue also has clinical implications. Electroencephalograms, or EEGs, which rely on arrays of scalp electrodes to record brain activity, are common clinical tests used to make diagnoses for such diseases as epilepsy. If the electrodes don’t work well, diagnoses could be harder 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.”

When undergraduate student Arnelle Etienne joined Grover’s laboratory, 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.

EEG technicians try to “MacGyver” their way through, sometimes by asking patients to straighten or steam their hair before the tests, Etienne says. But those workarounds aren’t ideal, especially if EEG measurements are needed quickly. “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 undergraduate 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, a measurement of resistance to the electrical current. A good EEG signal is considered to have less than 50 kilo-Ohms of impedance; unbraided, curly hair with standard electrodes yielded 615 kilo-Ohms.

To get a closer connection with the scalp, braiders created tight, thin cornrows that left study participants’ scalp exposed in strategic spots. Along with the braids, the researchers developed flexible electrode clips, shaped like dragonfly wings, designed to push under the flanking braids. Etienne, whose father is Haitian, and her colleagues call the electrode “sevo,”after the Haitian-Creole word for “brain.”

Anchored by the sturdy braids, the clips moved the electrodes closer to the scalp and resulted in impedance measurements of 22.6 kilo-Ohms in tests on eight participants, the researchers report February 27 at BioRxiv.org. That was well within the range for a reliable EEG measurement.

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.”