Brain-computer interfaces can give paralyzed people back some of their mobility by controlling exoskeletons. However, more complex control signals cannot yet be read from the head surface because conventional sensors are not sensitive enough for this. This challenge has been addressed by a consortium of Fraunhofer IAF, Charité - Universitätsmedizin Berlin, University of Stuttgart and industrial partners: In the recently launched BMBF lighthouse project "NeuroQ", the project partners are developing highly sensitive diamond-based quantum sensors that will enable paralyzed people to control neural exoskeletons more precisely.
For people who, for example, cannot move their hands or legs due to a spinal cord injury, stroke or other illness, so-called brain-computer interfaces (BCIs) represent great hope: These brain-computer interfaces allow a device to be controlled using brain activity alone - for example, an exoskeleton can be controlled just by imagining movement. Thus, BCIs offer paralyzed people the chance to regain control over some of their ability to move.
A patient tests a brain-computer interface developed by Charité to control an exoskeleton hand.
BCIs that measure brain activity from the surface of the head have the advantage of sparing patients a costly and risky surgical procedure on the brain. "We have already developed a non-invasive BCI system that enables people with high paraplegia to grasp everyday objects by means of arbitrary changes in their brain waves," reports Prof. Dr. Surjo R. Soekadar, Einstein Professor of Clinical Neurotechnology at Charité, adding, "Despite the considerable progress, however, it has not yet been possible to control complex hand movements with such a non-invasive system." For example, although the intention to move can be detected, it is not possible to determine exactly which movement is to be executed. To achieve this, the sensitivity of the sensors would have to be significantly increased.
Quantum sensors measure brain waves
Nine partners have now taken on this task and launched the project "Laser Threshold Magnetometer for Neuronal Communication Interfaces", or "NeuroQ" for short. In the project, which is funded by the German Federal Ministry of Education and Research (BMBF), the project partners are developing quantum sensors that are so sensitive that they can measure the smallest magnetic fields generated by brain waves. These quantum magnetometers are to be integrated into a BCI system and thus enable paralyzed persons to control a hand exoskeleton much more precisely than is currently the case.
Magnetic fields provide clearer signals
In non-invasive BCIs, the measurement of neuronal activity has so far mainly been carried out via electric fields. Here, the measurement of magnetic fields brings considerable advantages: "Magnetic fields penetrate the skin and skull undistorted and thus provide much clearer signals than electric fields, since these are strongly attenuated on the way from the source to the sensor. Thus, magneto-encephalography (MEG) has significant advantages over electroencephalography (EEG), but is rarely used due to technical hurdles," explains Dr. Jan Jeske, project leader of "NeuroQ" and researcher at Fraunhofer IAF.
The technical hurdles of MEGs are due to the sensor technologies used: SQUID sensors (Superconducting Quantum Interference Devices) are highly accurate, but require cryogenic cooling, which makes their use extremely expensive and complex. Optically pumped magnetometers (OPMs) based on vapor cells even surpass the sensitivity of SQUIDs, but they only work in the absolute zero field - this means that for their operation any background magnetic field (including the earth's magnetic field) must be completely shielded, which also entails an enormous construction effort.
"So far, no magnetometers have been realized that achieve a sensitivity under ambient conditions - i.e. in unshielded environments - that would be suitable for the detection of neuromagnetic fields. The 'NeuroQ' project considerably surpasses the state of the art," summarizes Prof. Dr. Jörg Wrachtrup, head of the 3rd Institute of Physics at the University of Stuttgart.
Diamond-based sensor allows use in everyday environment
The special feature of the quantum magnetometers to be developed in the "NeuroQ" project is their starting material: they are based on NV (nitrogen-vacancy center) centers in diamond and thus have unique properties: Diamond quantum magnetometers are the only highly sensitive magnetometers that function at room or body temperature. They also measure in the presence of a background magnetic field and can determine the exact direction of a magnetic field (i.e., all three components of the vector). In addition, they are biocompatible and can be brought close to the source, which in turn allows for stronger signals.
All this leads to the perspective that diamond quantum magnetometers could be used in clinics, surgeries, a rehabilitation environment, but also at home and in everyday life to significantly improve the quality of life of paralyzed people and make an important contribution to their social inclusion.
Multidisciplinary joint project
Since the diamond magnetometers developed so far do not yet achieve the required sensitivity, new highly sensitive quantum magnetometers based on a novel NV diamond laser will first be realized within the framework of "NeuroQ". The measurement system will then be developed with the required communication interface to a BCI system and used for demonstration, evaluation and further development in the clinical environment at the Charité in Berlin. The participating start-ups and small and medium-sized enterprises (SMEs) are making a significant contribution not only to the development but also to the subsequent exploitation of the technology, thereby promoting the transfer of the results into marketable products and applications.
The BMBF is funding the five-year collaborative project as part of the measure "Lighthouse projects in quantum-based metrology to meet societal challenges" with a total of almost 9 million euros.
The project partners at a glance:
- Fraunhofer Institute for Applied Solid State Physics IAF
- Twenty-One Semiconductors
- University of Stuttgart, 3rd Institute of Physics
- Sacher Laser Technology GmbH
- Advanced Quantum Ltd.
- W+R Shielding Technology GmbH
- Charité - University Medicine Berlin
- neuroConn GmbH
- NIRx Medical Technology Ltd.
Source: Fraunhofer IAF
Prof. Dr. Jörg Wrachtrup, University of Stuttgart, 3rd Institute of Physics, Tel. +49 711 685 65278, E-mail