uni'wissen 02(4)-2011_ENG

in” to what the neurons have to say to each other. Probes are still used primarily for pure research, but in the near future they could open up many new possibilities for clinical practice – for in- stance in further refined deep brain stimulation for patients suffering from Parkinson’s disease, a technique with which 75,000 patients around the world have already been successfully treated. The great advancements in research in this area are the result of NeuroProbes, a four-year project funded by the European Union that ended in 2010. In addition to neuroscientists and clients from industry, the 14 partners from ten European countries also included technology experts like those at Oliver Paul’s laboratory. IMTEK received 2.25 million of the 13 million euros in funding for the project. Patrick Ruther was in charge of tech- nological coordination. According to Paul, Neuro- Probes clearly reached its goal, namely to end European dependence on American providers: “We have caught up with and even passed them in some areas.” As far as he knows, no one else has succeeded in installing 200 electrodes on a shaft with a width of only 0.1 millimeters. The fact that IMTEK employs specialists for optics, fluid- ics, and electronics who know how to produce custom-fitting probes from CD-sized silicon disks using chemical methods like the dry etching tech- nique played out to the scientists advantage. Even a Hair’s Breadth Off is Too Much The probes are not ready made but always customized to client specifications. Research groups from Charité in Berlin, the Max Planck In- stitute in Frankfurt, and the universities of Tübin- gen, Cambridge, Freiburg, and even Berkeley order probes from IMTEK. The University of Further Reading Seidl, K./Herwik, S./Torfs, T./Neves, H. P./Paul, O./ Ruther, P. (2011): CMOS-Based High-Density ­Silicon Microprobe Arrays for Electronic Depth Control in Intracortical Neural Recording. In: Journal of Microelectromechanical Systems (in press), DOI: 10.1109 /MEMS.2011.2167661. Ruther, P./Herwik, S./Kisban, S./Seidl, K./Paul, O. (2010): Recent Progress in Neural Probes Using Silicon MEMS Technology. In: IEEJ Transactions on Electrical and Electronic ­Engineering 5/5, ­ p. 505 – 515. Herwik, S./Kisban, S./Aarts, A./Seidl, K./­ Girardeau, G./Benchenane, K./Zugaro, M./ Wiener, S./Paul, O./Neves, H. P./Ruther, P. (2009): Fabrication technology for silicon- based microprobe arrays used in acute and sub-chronic neural ­recording. In: Journal of ­Micromechanics and Microengineering 19/7, 074008 (11 Seiten). Electrodes in action: The magnetic resonance image shows a rat’s brain with ­implanted probes from the Department of Microsys- tems Engineering. The red curves show the behavior of electrical signals (in ­millivolts) over time (in seconds), as measured at various positions. Image: University of ­Cambridge/Holtzman 6 uni'wissen 04 on razor-thin conductor paths. From there they reach the outside by way of a highly flexible rib- bon cable or a wireless connection. More Than Just Random Noise Another reason why the body’s control center is no longer terra incognita for neuroscientists is the development of external measuring methods like electroencephalography and magnetic reso- nance imaging. “They provide us with a compar- atively large-scale image of what happens in- side,” says Paul. Ruther likens such methods to a microphone held up in front of a big crowd of people. “It picks up a general murmuring and other random noise, but you can’t hear individual voices.” This is precisely what the invasive meth- ods are supposed to detect. The scientists apply entire networks of electrodes directly to the cor- tex to obtain more precise results. The elec- trodes on the neural probes are spaced approxi- mately one-twentieth of a millimeter from one another, a distance which corresponds roughly to the spaces between nerve cells. By register- ing the electric current that passes from one nerve cell to another, the researchers can “listen probe shafts2mm