Final answer:
Henry Molaison, known as H.M., had his medial temporal lobes, including his hippocampi and amygdala, removed during a lobotomy to control seizures, resulting in anterograde amnesia.
Step-by-step explanation:
The part of H.M.'s brain that was removed during his lobotomy was both the left and right medial temporal lobes, which included the hippocampi and amygdala. This procedure was initially performed to alleviate H.M.'s severe seizures. However, this led to H.M. developing anterograde amnesia, meaning he could no longer form new memories, despite retaining the ability to recall many events that occurred before the surgery. Additionally, he experienced partial retrograde amnesia, which affected some of his earlier memories. H.M.'s case became a seminal instance in the study of the relationship between brain structure and memory function.