Stimulation of various areas of the limbic and hypothalamic regions in the Macaca mulatta resulted in a variety of responses. These responses were compared with those obtained on stimulating areas of the mid-brain reticular formation.It would appear that "overlapping" occurs as to the function of the limbic system, the mesencephalic reticular formation and the hypothalamus, in view of the similarity of behavior patterns elicited by stimulating some areas in these three different regions.The EEG patterns from the limbic, reticular (mesencephalic) and hypothalamic systems varied significantly so as to suggest that each system may function basically as an individual component system of the brain, probably influenced by ramifications one with the other. This EEG study is a preliminary investigation.Abstract Teaser