Serving multiple useful purposes, brain-computer interfaces (BCIs) usually incorporate scalp-applied or even brain-implanted electrodes. A new, less-invasive BCI, however, can simply be placed in the patient’s ear canal.
Developed by a team of scientists from China’s Tsinghua University, the experimental device is known as the SpiralE. Measuring just 50 mm long by 3 mm wide, it takes the form of a thin multilayered rectangular strip made up of two shape-memory polymer layers, one electrothermal actuation layer, and one EEG (electroencephalogram) layer. The strip is initially tightly curled like a corkscrew, allowing it to be easily inserted into the patient’s wider ear canal.
Once the device is in place, it’s exposed to an external electrical field, triggering a Joule heating process in its electrothermal actuation layer. The heat which is generated causes the strip’s shape-memory polymers to try reverting to a flat, non-curled state. The strip starts to uncurl, but it stays held in a less-tightly-curled configuration by the inner walls of the ear canal. Its EEG electrode layer is thus pressed up against the ear-canal skin, where it can detect the brain’s electrical signals.
Because the device expands to the constraints of each person’s uniquely shaped ear canal, it always provides a custom fit. And as it’s essentially a hollow spiral, it doesn’t block sound waves and won’t affect the patient’s hearing. Removing it is simply a matter of gently pulling and twisting it out.
In lab tests, the device was found to be comfortable to wear for prolonged periods, and it proved to be up to 95 percent accurate at detecting volunteers’ brain activity. The scientists hope that it may ultimately find use in applications such as detecting epilepsy, drowsiness, or monitoring patients’ sleep patterns.
A paper on the research, which was led by Zhouheng Wang, was recently published in the journal Nature Communications.