Working Paper Experimental Social Sciences Experimental Social Sciences The Cognitive Processing of Altruistic and Spiteful Behavior: An fMRI Study May, 2009 Grant-in-Aid for Scientific Research on Priority Areas ExpSS-E-10 Tsuyoshi Nihonsugi Institute of Social and Economic Research, Osaka University, JSPS Research Fellow/ISER, Osaka University Takafumi Yamakawa Institute of Social and Economic Research, Osaka University Jun Shinozaki Institute of Social and Economic Research, Osaka University, Department of System Neuroscience, School of Medicine, Sapporo Medical University Makoto Kato Kobe Advanced ICT Research Center Kenju Akai JSPS Research Fellow/ISER, Osaka University Takuma Wakayama Faculty of Economics, Ryukoku University Tsutomu Murata Kobe Advanced ICT Research Center Tatsuyoshi Saijo Institute of Social and Economic Research, Osaka University Toward Experimentally-based New Social Sciences for the 21st Century