HM meaning in General ?

Henry Gustav Molaison (February 26, 1926 – December 2, 2008), known widely as H.M., was an American man who had a bilateral medial temporal lobectomy to surgically resect the anterior two thirds of his hippocampi, parahippocampal cortices, entorhinal cortices, piriform cortices, and amygdalae in an attempt to cure his epilepsy. Although the surgery was partially successful in controlling his epilepsy, a severe side effect was that he became unable to form new memories.

The surgery took place in 1953 and H.M. was widely studied from late 1957 until his death in 2008. He resided in a care institute in Windsor Locks, Connecticut, where he was the subject of ongoing investigation. His case played an important role in the development of theories that explain the link between brain function and memory, and in the development of cognitive neuropsychology, a branch of psychology that aims to understand how the structure and function of the brain relates to specific psychological processes.

Molaison's brain was kept at University of California, San Diego where it was sliced into histological sections on December 4, 2009. It was later moved to The M.I.N.D. Institute at UC Davis. The brain atlas constructed was made publicly available in 2014.