Final answer:
After surgery, HM developed anterograde amnesia and lost the ability to form new memories. However, his working memory remained intact.
Step-by-step explanation:
H.M., who had epileptic seizures, underwent a bilateral lobectomy in 1953 to alleviate his seizures. As a result, he developed anterograde amnesia, which means he was unable to form new memories. However, his short-term memory, also known as working memory, remained intact. After a brief period, these memories would dissipate or decay because the structures in his medial temporal lobes responsible for long-term memory storage were removed.