Brain signals can be read using soft, flexible, wearable electrodes that stick onto and near the ear like a temporary tattoo and can stay on for more than two weeks even during highly demanding activities such as exercise and swimming, researchers say.
The invention could be used for a persistent brain-computer interface (BCI) to help people operate prosthetics, computers, and other machines using only their minds, scientists add
For more than 80 years, scientists have analyzed human brain activity non-invasively by recording electroencephalograms (EEGs). Conventionally, this involves electrodes stuck onto the head with conductive gel. The electrodes typically cannot stay mounted to the skin for more than a few days, which limits widespread use of EEGs for applications such as BCIs
Now materials scientist John Rogers at the University of Illinois at Urbana-Champaign and his colleagues have developed a wearable device that can help record EEGs uninterrupted for more than 14 days. Moreover, their invention survived despite showering, bathing, and sleeping. And it did so without irritating the skin. The two weeks might be "a rough upper limit, defined by the timescale for natural exfoliation of skin cells," Rogers says.
The device consists of a soft, foldable collection of gold electrodes only 300 nanometers thick and 30 micrometers wide mounted on a soft plastic film. This assemblage stays stuck to the body using electric forces known as van der Waals interactions—the same forces that help geckoes cling cling to walls.
The electrodes are flexible enough to mold onto the ear and the mastoid process behind the ear. The researchers mounted the device onto three volunteers using tweezers. Spray-on bandage was used once twice a day to help the electrodes survive normal daily activities.
The electrodes on the mastoid process recorded brain activity while those on the ear were used as a ground wire. The electrodes were connected to a stretchable wire that could plug into monitoring devices. "Most of the experiments used devices mounted on just one side, but dual sides is certainly possible," Rogers says.
The device helped record brain signals well enough for the volunteers to operate a text-speller by thought, albeit at a slow rate of 2.3 to 2.5 letters per minute