Answer: Most likely, the surgery destroyed a portion of the hippocampus in Darnell's brain.
Step-by-step explanation: The hippocampus is a part of the human brain. It is located in the medial temporal lobe of the brain. Moreover, the hippocampus has an important function since it is the part of the brain responsible for forming new episodic memories. Henry Gustav Molaison was a famous American patient who suffered from epilepsy and decided to undergo surgery to cure it; however, his condition got worse because his hippocampus was destroyed during the surgery. As a result, although Molaison continued to remember event from the past, he was unable to storage new memories from that moment onwards, which upheld the theory of an existing relationship between the hippocampus and the formation of new memories.