Final answer:
Henry Molaison (HM) suffered from anterograde amnesia and partial retrograde amnesia after a surgery to cure his epilepsy, preventing him from forming new episodic memories but retaining some short-term and procedural memory abilities.
Step-by-step explanation:
After the bilateral lobectomy surgery to alleviate epilepsy, Henry Molaison, known as patient HM, developed anterograde amnesia and a partial retrograde amnesia. The removal of the medial temporal lobes which included areas such as the hippocampus and amygdala, prevented HM from forming new episodic memories, though he retained the ability to remember past events and maintain short-term memory for a brief period. HM's procedural memory remained intact, demonstrated by his ability to get better at tasks such as puzzles despite not recalling having done them before.