 MacLean believed that there was a connection between a human's violent actions and rational behaviour.Further achievements of MacLean, was coining the idea of the limbic system, the set of brain structures that surround the hypothalamus and are responsible for human emotions, memories and arousal.The research made by MacLean was based off previous studies by Dr James Papez, a neuroscientist that during the 1930s and 1940s, delved into the circuit between the hippocampus, thalamus and cingulum, and how their connection is the basis for human emotion.