[1] CNR, Inst Cognit Sci & Technol, I-00185 Rome, Italy
[2] Positron Emiss Tomog Ctr IRMET SpA, Turin, Italy
[3] CTO Hosp, Dept Neuroradiol, Turin, Italy
[4] Univ Turin, ALS Ctr, Dept Neurosci, Turin, Italy
[5] Univ Genoa, Clin Neurophysiol Unit, Dept Neurosci, Genoa, Italy
[6] Univ Genoa, Dept Internal Med, Nucl Med Unit, I-16126 Genoa, Italy
[7] Inst Cognit Sci & Technol, Padua, Italy
[8] Karolinska Hosp, Dept Nucl Med, S-10401 Stockholm, Sweden