Complex sentence: Thier served as President of the Institute of Medicine, National Academy of Sciences, from 1985 to 1991 and President of Brandeis University from 1991 to 1994.
Split into simpler sentences: Thier served as President of the Institute of Medicine, National Academy of Sciences, from 1985 to 1991. Thier was the President of Brandeis University from 1991 to 1994.