1. Research Laboratory of Electronics and McGovern Institute for Brain Research Massachusetts Institute of Technology Cambridge MA 02139 USA
2. Department of Biomedical Engineering Faculty of Engineering Tel Aviv University Tel Aviv 6997801 Israel
3. Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology Cambridge MA 02139 USA
4. Department of Materials Science and Engineering Massachusetts Institute of Technology Cambridge MA 02139 USA
5. Department of Brain and Cognitive Sciences Massachusetts Institute of Technology Cambridge MA 02139 USA