Wearable EEG patch records stable brain signals over 24 hours, including sleep

Reliably recording brain activity over many hours has so far been fraught with technical and practical challenges. While traditional electroencephalography (EEG) systems provide meaningful data, they are often uncomfortable and typically limited to controlled testing environments. Is it even possible to record EEG signals with good signal quality in everyday situations?

The Mobile Neurotechnologies group at the Fraunhofer Institute for Digital Media Technology IDMT in Oldenburg has an answer to this question. The group is developing a discreet EEG sensor solution for mobile use. In a recently published study in the journal Sensors, the researchers show that the system delivers stable EEG data for at least 24 hours a day, both day and night.

Flexible electrode patch meets miniature amplifier

For the study, 10 participants were fitted with the flexible, eight-channel electrode patch “trEEGrid,” developed at Fraunhofer IDMT in Oldenburg. Thanks to the pre-applied conductive material, the patented patch can be applied to the face just like a Band-Aid and, unlike dry electrode systems, does not exert any pressure on the head to ensure good signal quality.

The electrode patch was combined with a special miniaturized signal amplifier. It is connected to the patch directly behind the ear, making the system less sensitive to interference caused by cable movement. Power is supplied by a base unit that is carried in a waist or chest pocket and barely restricts freedom of movement.

Meaningful measurement data—even after sleep

While the electrode patch was worn continuously for about 24 hours, the study participants completed several short auditory and visual stimulation tasks, relaxation exercises and Sudoku puzzles. At night, their sleep was recorded in their own bedrooms. The team regularly monitored the quality of contact between the electrodes and the skin based on resistance, known as impedance. Conventional ring electrodes were freshly applied for each comparison measurement.

The analyses show that, with a few exceptions, the “trEEGrid” maintained very stable contact throughout the entire period. The average impedance values for all participants were below 140 kOhm for all eight channels on the first day and even below 100 kOhm on the second day. Even after overnight recording, the electrode patch remained securely in place. Typical patterns and responses from the tasks presented could be identified in the subsequent data analysis. For example, the signals clearly distinguished between the easy and difficult Sudoku levels.

“Our current sensor solution already captures EEG signals in basic everyday situations with high contact stability. It can be worn much more discreetly, is significantly more comfortable and can therefore be used for longer periods than traditional systems,” explains Dr.-Ing. Insa Wolf, head of Mobile Neurotechnologies at Fraunhofer IDMT. “The system and our feasibility study open up a completely new approach to recording and interpreting brain activity data.”

A strong partnership on the path to the EEG lab to go

Brain Products GmbH developed the prototype miniature amplifier used in the 24-hour study specifically to meet the requirements of Fraunhofer IDMT. The internationally active company, headquartered in Gilching, Germany, specializes in hardware and software for neurophysiological research.

Both partners are currently collaborating on the research project “ISES—Interactive sleep monitoring system for the early detection of gender-specific sleep disorders.” Among other goals, the project aims to extend the battery life of the sensor system and add sensors to record movements as important contextual information.

Since the current study deliberately included participants from the research team itself, the next step is to test the Fraunhofer IDMT EEG system with a more diverse group of participants without prior specialized knowledge. Fraunhofer IDMT is also expanding its tests to dynamic everyday situations: the system has already provided initial meaningful EEG signals while walking and cycling. To analyze this novel long-term data, AI-based methods are being developed for interpreting and automatically filtering out interference signals such as eye and muscle movements.

Fraunhofer IDMT’s goal is to use realistic, long-term data on brain activity to provide important insights into people’s health status—for example, to better investigate sleep disorders, daytime sleepiness or neurodegenerative diseases in the future. The automatic documentation of epileptic seizures and research into neurological correlations in diseases such as ME/CFS are also among the key areas of focus. Furthermore, in-vehicle or cockpit assistance systems could be evaluated more thoroughly by tracking sustained attention and fatigue.

Provided by
Fraunhofer Institute for Digital Media Technology IDMT

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