He
finished his secondary education in Horten in 1917 and studied at the
Royal Frederick University, graduating with the
cand.med. degree in 1924. He was hired as a
prosector there in 1926, studied with a
Rockefeller Grant under
C. Judson Herrick at the
University of Chicago from 1927 to 1929, and back in Norway he took the
dr.med. degree in 1931 with the thesis
The brain of Myxine glutinosa. He continued as a researcher at the University of Chicago, and was a professor from 1945 to 1966. He was the Europe-based editor for the
Journal of Comparative Neurology. Together with
Alf Brodal he is credited with founding the "Oslo School" of brain research. His research speciality was the
cerebellum, but in addition to the human brain, Jansen did research on
cetacean brains. He also did research in
neuropathology and published textbooks in anatomy and histology, and published three books based on
Olof Larssell's work after Larssell died. He edited the
illegal newspaper Bulletinen from 1941; from 1942 to 1944 as the sole editor, and was a member of the so-called Coordination Committee ( (KK)). He had to flee to Sweden in 1944. Jansen was decorated Commander of the
Royal Norwegian Order of St. Olav in 1963. He was a member of the
Norwegian Academy of Science and Letters, and an
honorary doctor of the
University of Kiel, the
University of Leiden and the
University of Århus. ==Selected bibliography==