MacLean originally formulated the triune brain hypothesis in the 1960s, drawing on comparative neuroanatomical work done by Ludwig Edinger, Elizabeth C. Crosby and Charles Judson Herrick early in the twentieth century.[4][5] The 1980s saw a rebirth of interest in comparative neuroanatomy, motivated in part by the availability of a variety of new neuroanatomical techniques for charting the circuitry of animal brains. Subsequent findings have refined the traditional neuroanatomical ideas upon which MacLean based his hypothesis.