[1] Univ Bordeaux 2, Interdisciplinary Inst Neurosci, Unite Mixte Rech 5297, F-33000 Bordeaux, France
[2] CNRS, Interdisciplinary Inst Neurosci, Unite Mixte Rech 5297, F-33000 Bordeaux, France
[3] Commissariat Energie Atom Saclay, Inst Rech Lois Fondamentales Univers, Serv Astrophys, Serv Elect Detecteurs & Informat, F-91191 Gif Sur Yvette, France
[4] Stanford Univ, Dept Math, Stanford, CA 94305 USA
[5] Stanford Univ, Dept Stat, Stanford, CA 94305 USA
[6] Stanford Univ, Dept Elect Engn, Stanford, CA 94305 USA
[7] Univ Paris 06, Ecole Normale Super, CNRS, Lab Kastler Brossel,Unite Mixte Rech 8552, F-75005 Paris, France