Abstract
Certain brain areas show higher activity during the resting state than during the cognitive task performance. These areas are called “default brain areas” (DBA) and consist of mainly medial brain areas including medial prefrontal, anterior cingulate, posterior cingulate and precuneus areas. DBA is proposed to be concerned with “internal thought processes” which is supported by language, and considered to be not existent in animals. However, recent studies indicate that default brain activity is observed in nonhuman animals including the chimpanzee, macaque monkey and rat, suggesting that there might be primitive internal thought processes that do not need language in animals. It has been indicated that DBA is greatly overlapped with “social brain” that is concerned with processing social stimuli and coordinating appropriate social behavior in the human. It has been shown that nonhuman animals have a certain kinds of social behavior such as deceptive and altruistic behavior, and many areas in the animal DBA are also concerned with social behavior. Thus, DBA is thought to be concerned with internal thought processes regarding social behavior.
