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New prosthetic methods

All movements – each grip and step – have their origin in the brain. Carsten Mehring and his group at the Bernstein Centre for Computational Neuroscience and the Institute for Biology I at the University of Freiburg plan to use brain signals for the control of prostheses or for the operation of computers in order to create the basics for developing a prosthesis control for severely paralysed patients.

Working with colleagues from the University Hospital in Freibug, Mehring and colleagues from the Bernstein Centre were able to show that electrodes attached to the brain surface enabled the prediction of continuous arm movements. The findings have been published in the January issue of the “Journal of Neuroscience Methods” (Journal of Neuroscience Methods, 2008 Jan 15 167/1 pp. 105-114. doi: 10.1016/j.jneumeth.2007.10.001). Mehring’s team used a semi-invasive method, electrocorticography (ECoG), to measure the brain signals. ”This is an excellent compromise between fully-invasive and non-invasive methods,” explains Mehring. In non-invasive methods (e.g., EEG), the electrical activity produced by the brain is recorded by electrodes placed on the scalp. The neural signal has therefore little spatial resolution. In fully-invasive methods, the electrodes are implanted a few millimeters deep into the brain in order to record the activity of individual neurons or groups of neurons. The signal is a lot more accurate than that of non-invasive methods and is sufficient to control complex movements. Initial clinical studies involving severely paralysed patients have already been carried out to test this method. It is still difficult to assess the potential damage to the brain caused by the implanted electrodes or the stability of the measured signals over time.
Left: Example of a test run – volunteers moved a cursor (green) with their hand along a number of points (yellow) displayed on a screen. The volunteers could not see the course of the cursor and the points passed. Right: cursor movement along the X axis (top) and the Y axis (below) in a typical experiment (green curve). The movement reconstructed from the brain activity measured is shown in red.
Left: Example of a test run – volunteers moved a cursor (green) with their hand along a number of points (yellow) displayed on a screen. The volunteers could not see the course of the cursor and the points passed. Right: cursor movement along the X axis (
Left: Example of a test run – volunteers moved a cursor (green) with their hand along a number of points (yellow) displayed on a screen. The volunteers could not see the course of the cursor and the points passed. Right: cursor movement along the X axis (top) and the Y axis (below) in a typical experiment (green curve). The movement reconstructed from the brain activity measured is shown in red. (Photo: Carsten Mehring)
ECoG signals are recorded with electrodes placed directly on the exposed surface of the brain to record the electrical activity caused by large groups of neurons from the cerebral cortex. This method is less invasive than fully-invasive methods. It is also assumed that the measured signals are stable over a longer period of time. “We intend to test whether this method is suitable for controlling movement and hence represents a potential alternative for fully-invasive methods,” explains Mehring adding that, “Our results lead us to hope that it will work.”

Mehring conducted his examinations on epilepsy patients who had already had electrodes implanted below the surface of the skull prior to brain surgery. Mehring was able to use the same electrodes to record the patients’ brain activity while they operated a handle to move a cursor along specific points on the screen. The scientists used mathematical algorithms to extract brain signals from these measurements, which correlated with the movement of the cursor and enabled the continuous reconstruction of the movement.

In the next step, Mehring and his colleagues plan to investigate whether this strategy can be used to control a cursor on the screen with neuronal activity alone, without the patient moving their arm. “Previous studies have shown that the reconstruction of the movement from the brain signals can be further improved because the volunteer can learn to adapt his or her brain activity to the control of the cursor,” said Mehring. “There is hope that, based on such methods, it will in future be possible to develop a prosthesis control or a communication tool for severely paralysed patients. However, many scientific and technological problems will have to be solved before the system is ripe for practical application.

Source: Press Office University of Freiburg-17.01.2008
The Bernstein Centres for Computational Neuroscience in Berlin, Freiburg, Göttingen and Munch are funded by the German Federal Ministry of Education and Research (BMBF). Computational neuroscience combines experiments, computer simulation and theory construction in order to investigate the complex structure of the brain.
Further information:

Dr. Carsten Mehring
Institute for Biology I and Bernstein Centre for Computational Neuroscience
Tel.: +49 (0)761/203-2543
E-mail: mehring@biologie.uni-freiburg.de

Tobias Pistohl
Institute for Biology I and Bernstein Centre for Computational Neuroscience
Tel.: +49 (0)761/203-2580
E-mail: pistohl@biologie.uni-freiburg.de
Website address: https://www.gesundheitsindustrie-bw.de/en/article/news/new-prosthetic-methods