It became clear that his brain had been radically altered
The surgery occurred in 1953, and as H .M. healed, his seizures slowed. Almost immediately, however, it became clear that his brain had been radically altered. H.M. knew his name and that his mother was from Ireland. He could remember the 1929 stock market crash and news reports about the invasion of Normandy. But almost everything that came afterward-all the memories, experiences, and struggles from most of the decade before his surgery-had been erased. When a doctor began testing H.M.’s memory by showing him playing cards and lists of numbers, he discovered that H.M. couldn’t retain any new information for more than twenty seconds or so.