Who was H.M., and what did we learn about memory from his experiences?

Question

What will be an ideal response?

Answer 1

H.M. was a patient who underwent surgery to alleviate his seizures. In surgery, doctors removed several structures that made up his temporal lobe. Because of this, H.M. suffered from anterograde amnesia and, to an extent, retrograde amnesia. Retrograde amnesia refers to the inability to remember events prior to the impairment or brain damage. Anterograde amnesia involves the inability to form new memories after the impairment or brain damage. We learned that the hippocampus, one of the main structures that were removed from H.M., is considered one of the most important structures that play a role in storage and some retrieval of memories. It is responsible for the formation and consolidation of new memories and activates the retrieval of information as far back as 2 years. Research has also found that specific parts of the hippocampus also have specific roles. For example, the CA1 area provides the primary output from the hippocampus to other brain structures. Damage to CA1 results in moderate anterograde amnesia and minimal retrograde amnesia. Damage to entire hippocampal formation, which is made up of the hippocampus and nearby structures, results in retrograde amnesia that affects memory as far back as 15 or more years. Retrograde amnesia affecting memory for more extensive periods of time is due to damage to other cortical areas, suggesting that long-term memory is stored in other parts of the cortex. H.M. also shows evidence of this, as he was able to remember several events from his childhood. In addition, H.M. taught us that there are two types of memories - declarative and nondeclarative. His amnesia was a loss of declarative memory (memories for facts and events), but nondeclarative memory (memories for behaviors such as skills learning) was still intact, suggesting that these two types of memories are processed in different parts of the brain.