[3] Henschen went to Brazil, staying with Swedish physician and botanist Anders Fredrik Regnell; he conducted botanical research in Caldas from 1867 to 1869.

He later published Études sur le genre Peperomia comprenant les espèces des Caldas (in Nova Acta Regiae Societatis Scientiarum Upsaliensis, ser.

From 1878, he worked in the institute of pathology at the University of Uppsala, while in the meantime, he practiced medicine at a summer resort at Ronneby in Blekinge.

Henschen then continued his education in Leipzig under Carl Ludwig,[4] receiving his doctorate in medicine in 1879 and publishing his dissertation Om indigosvafvelsyradt natrons avsöndring i njurarna (On the renal excretion of indigo sulfuric acid in the kidneys), for which he was awarded a prize by the Swedish Medical Society.

"[6] His Klinische und anatomische Beiträge zur Pathologie des Gehirns (Clinical and anatomical contributions to the pathology of the brain) was published in over 25 editions from 1890 to 1930.

His extensive output also includes Über die Hörsphäre (1916), awarded the Florman Prize and the Retzius Gold Medal, Zur Kenntniss der Migräne (1913), Erfahrungen über Diagnostik und Klinik der Herzklopfenfehler (1916), awarded the Medical Society's Alvarenga Prize, I alkoholfrågan (1913), Om hjernans byggnad ock verksamhet (1921).

In addition, he published a number of small papers on various areas of internal medicine, both in the proceedings of the Uppsala Medical Association and in foreign journals.

In 1919 he described dyscalculia, and later introduced the term acalculia to define the impairment of mathematical abilities in individuals with brain damage (1925).