Final answer:
Procedural memory is the type of long-term memory not affected by hippocampal damage, and it allows individuals to remember how to perform tasks and skills. This was evident in patient H.M., who, despite his anterograde amnesia, could improve in tasks through procedural learning.
Step-by-step explanation:
Type of Long-Term Memory Not Affected by Hippocampal Damage
The type of long-term memory not affected by hippocampal damage, such as in the case of patient H.M., is known as procedural memory. Procedural memory involves the recall of how to perform tasks and skills, such as riding a bike or solving a puzzle. Despite H.M.'s extensive hippocampal damage, which led to anterograde amnesia and rendered him unable to form new episodic or semantic memories, he was still able to form new procedural memories. For instance, H.M. displayed improvement in completing certain tasks over repeated trials without the conscious memory of ever learning or performing such tasks.
Procedural memory is distinct from episodic and semantic memory as it resides in different brain structures outside the medial temporal lobe, such as the cerebellum and the basal ganglia. This explains why, even after the removal of hippocampal and amygdala regions, procedural memory can remain intact and functional. H.M.’s ability to acquire new procedural memories without hippocampal involvement provides key insights into the diverse neurological pathways governing memory.