What part of H.M.'s brain was damaged and what memory problem did this cause him?

H.M., known in medical literature as Henry Molaison, was a patient who suffered from severe epilepsy. In an attempt to control his seizures, he underwent a surgical procedure in 1953, performed by neurosurgeon William Scoville. During the surgery, parts of H.M.'s brain were removed, including the medial temporal lobe structures of the hippocampus, the entorhinal cortex, and parts of the amygdala.

The removal of these areas caused H.M. to develop a profound memory disorder. Specifically, he suffered from anterograde amnesia, which is the inability to form new long-term memories. While H.M. retained his short-term memory and could remember events from his past prior to the surgery, he was unable to create new lasting memories after the procedure. This meant that he could not remember new people he met, new experiences he had, or anything he learned after the surgery for more than a few moments.

H.M.'s case was extensively studied by cognitive psychologists and neuroscientists, including Brenda Milner and Suzanne Corkin, and it provided critical insights into the functioning of the human memory system. His case was pivotal in demonstrating the role of the hippocampus and related structures in the consolidation of new memories, shaping our understanding of how memories are formed and stored in the brain.