Economists have been using game theory to study decision-making since the 1950s. More recently, the interdisciplinary field of neuroeconomics has gained popularity as scientists try to understand how economic decisions are made in the brain. Researchers led by Professor Masayuki Matsumoto and Assistant Professor Hiroshi Yamada at the University of Tsukuba in Japan studied populations of neurons across the monkey brain reward network to find out where and when expected value is calculated.