Final answer:
Following a bilateral lobectomy, HM experienced anterograde amnesia, losing the ability to form new memories, and retrograde amnesia, losing some past memories, yet maintained short-term memory.
Step-by-step explanation:
Henry Molaison, known as patient HM, underwent a bilateral lobectomy to treat his epilepsy, which resulted in a significant change in his memory functions. After the surgery, HM lost the ability to form new memories, known as anterograde amnesia. He was also affected by retrograde amnesia, which led to a partial loss of memories prior to the operation. Despite these losses, HM retained his short-term memory, although this did not convert into long-term memories due to the removal of structures in the medial temporal lobes. His case provided important insights into the differences between episodic memory and procedural memory, as well as the role of the medial temporal lobes in memory storage.