Final answer:
Brenda Milner discovered through studying H.M. that there are different memory systems, such as procedural and episodic memory, and that the hippocampus is essential for forming new long-term memories.
Step-by-step explanation:
Two of Brenda Milner's significant discoveries about memory that resulted from studying patient H.M. include the differentiation between different types of memory and the specific role of the hippocampus in memory formation. The first discovery was that there are multiple memory systems in the brain, evidenced by H.M.'s ability to retain procedural memory (how to perform tasks) despite his inability to form new episodic memories (autobiographical events). The second discovery was the role of the medial temporal lobe, especially the hippocampus, in the consolidation of new long-term memories, which was inferred from H.M.'s inability to form new long-term memories after his hippocampus was removed. Through her work with H.M., Milner provided crucial insights into the processes of memory storage and retrieval.