Final answer:
Henry Molaison, or H.M., lost the ability to form new long-term episodic memories, which is known as anterograde amnesia, following the removal of his hippocampus. He could still form procedural memories and had intact short-term memory but could not consolidate new information into long-term memory.
Step-by-step explanation:
After Henry Molaison had his hippocampus removed to control his severe seizures, he lost his ability to form new declarative memories, a condition known as anterograde amnesia. Specifically, Henry Molaison, also known as H.M., was no longer able to form new episodic memories, which are autobiographical in nature. However, he retained the ability to remember past events prior to the surgery and could still form new procedural memories, which involve skills and tasks rather than specific events or facts.
The removal of H.M.'s hippocampus and related medial temporal lobe structures disrupted the normal process of consolidating short-term memories into long-term memories. Thus, while he could still hold temporary information in his short-term memory, he was unable to transfer those memories into long-term storage. Therefore, H.M.'s case illustrates the critical role the hippocampus plays in memory formation.