1. Department of Neuro- and Sensory Physiology, University of Goettingen, Humboldtallee 23, 37073 Goettingen, Germany. Center of Anesthesiology, University of Goettingen, Robert-KochStreet 40, 37075 Goettingen, Germany. Department of Anatomy, Kreuzbergring 36, 37075 Goettingen, Germany.