Final answer:
Hippocampal lesions primarily disrupt the ability to form new memories, leaving other types of memory that involve different brain areas unaffected.
Step-by-step explanation:
Hippocampal lesions disrupt the ability to form new memories. The hippocampus is a critical part of the brain's limbic system involved in memory formation, particularly with the consolidation of new declarative memories. Damage to this region results in difficulty or inability to process new information into long-term storage. Famous cases, like that of patient H.M., have illustrated this, where after having his medial temporal lobes (including the hippocampi) removed, he was no longer able to form new memories. It is important to acknowledge that other types of memory, such as procedural or implicit memory, involve different brain areas like the cerebellum and are not affected by damage to the hippocampus.