Projekts

Project I:
Human BMI-studies

started 2003

A major challenge in neuro-engineering today is to develop a brain-machine interface (BMI) suitable for restoring communication and motor control in paralyzed patients. In this project we are investigating the potential of epicortical field potentials (EFPs). These are the bioelectrical signals measured directly from the surface of the cerebral cortex that are used as a basis for BMIs, particularly for decoding parameters of voluntary hand and arm movement. Our results show that EFPs are a highly promising control signal for neuroprosthetics.

Obviously, direct recordings from the human brain using implanted electrodes are not possible under normal conditions. However, the temporary implantation of intracranial electrodes is required for medical diagnostic purposes in some patients. Primarily in order to determine the exact area of origin of epileptic seizures before surgically removing them. Provided the informed consent has been obtained from these patients they may take part in scientific experiments.

1. Position of a grid electrode over the left cerebral hemisphere as implanted for pre-neurosurgical diagnostics.
2. Intraoperatively taken photograph of subdural grid electrode implantation, showing the individual platinum electrode contacts. With kind permission from Ball et al., Biomed Tech (Berl), 2004.

The distance between brain surface and scalp surface is about 4cm. While intracranially measured signals reflect more local brain activity, the electroencephalogram (EEG) and the magnetencephalogramm (MEG) are neuronal mass signals which are obtained from the scalp surface reflecting the activity of whole brain areas.

Together with the MEG-Center at the University of Tuebingen, we are using the electroencephalogram (EEG) and magnetencephalogram (MEG) to back our intracranial measurements and to provide additional insights into oscillatory movement-related brain activity, neuronal correlates of sensorimotor learning and ongoing activity.

Sample references:

• Waldert S, Preissl H, Demandt E, Braun C, Birbaumer N, Aertsen A, Mehring C (2008) Hand movement direction decoded from MEG and EEG. Journal of Neuroscience 28(4):1000-1008 (PDF). Also available at: The Journal of Neuroscience, copyright: The Society for Neuroscience.
• Pistohl T, Ball T, Schulze-Bonhage A, Aertsen A, Mehring C (2007) Prediction of Arm Movement Trajectories from ECoG-Recordings in Humans, J Neurosci Methods, 167/1 pp. 105-115 (in press)