In 1966, charles whitman killed his wife, his mother, and 14 more people at the university of texas before he was killed by police. an autopsy revealed that a tumor affecting whitman's was likely the cause for the his killing spree.

The correct answers are amygdala and motivation. 
Amygdala is part of human brain responsible for many things, the most important of which (for your question) are decision-making and emotional response. Given that Whitman had a tumor which was affecting his amygdala, he couldn't really think straight and the motivation behind his crimes was likely due to this tumor. 

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Yes you are cute answer theories to explain the colonization of the new world the last great habitable landmass to be occupied by humans focus on the bering land bridge, or beringia, which emerge by siberia and alaska the last ice age.