Decision-making plays an important role in the transformation of incoming sensory information to purposeful actions. Many decisions have important biological and social consequences, while others may have a more limited impact on our everyday life. The neural mechanisms of decision-making currently constitute an important subject under intense investigation in the field of cognitive and behavioral neuroscience. Among the investigations, on this topic, those involving sensory discrimination tasks using visual motion have provided a wealth of information about the nature of the neural circuitry required to perform perceptual decision-making. For example, by using a motion discrimination task, Shadlen and Newsome have shown an essential role of area LIP in perceptual decision-making. On the other hand, the importance of reward and reward expectations as determinants of decision-making is increasingly appreciated. In particular, reinforcement learning and economic theories, such as game theory, have provided valuable insights into the brain functions related to decision-making. By using a competitive game analogous to matching pennies against a computer, Lee's group showed that in monkeys, previous selections modulated prefrontal neural activity and that this modulation affected the current choice behavior. The prefrontal cortex has been shown to participate in decision-making in free-choice conditions. By using a task involving the free choice of 1 target from multiple saccade targets, Funahashi's group examined the prefrontal participation in decision-making in a free-choice condition. They compared the activities of prefrontal neurons during an oculomotor delay task with forced-choice conditions and free-choice conditions and identified the neural components reflecting the underlying decision-making processes. Although several attempts have been made to understand the neural mechanisms of decision-making, further investigations are required to fully understand these mechanisms. Future studies should evaluate the effects of emotions on decision-making and attempt to integrate the neurophysiological, psychological, and computational approaches to decision-making.