According to the report, the removal of hippocampus and hippocampal gyrus selectively influences ability to acquire new explicit memories like episodic memory and semantic memory, which caused some patients (who lost approximately 8 cm from the temporal lobes, including H. M.) severe anterograde amnesia. At the same time it caused retrograde amnesia for events just before the surgery, but it was modest compared to anterograde one. However, the removal does not affect implicit memory such as working memory nor procedural memory. Therefore, patients could learn new motor skills, even though they were not able to remember the learning process. The selective effects on newer memory after the removal seems to partly explain the reason that patients
