When Susannah interviews Dr. Morrison in December 2010, she explains that brains create stories with fragments. She also mentions that smells or images can unlock memories that a person forgot, something Susannah experiences when a friend takes her to an Irish pub. Susannah remembers being there with Stephen before the Ryan Adams show. She vividly remembers being disgusted by her fish and chips, and wonders what else she's forgotten.
This particular memory of the Irish pub doesn't just help fill in Susannah's memory: it forces the reader to alter their own memory of reading the passage in question, as it was never specified that Susannah didn't actually remember that evening.
A year after she moves in with Stephen, Susannah begins unpacking boxes from her old apartment. She discovers a postcard in a little paper bag of a famous painting of a woman in profile, wearing a black dress. Susannah feels as though she recognizes it and pulls out her receipt. She'd purchased the postcard of the painting Madame X at the Metropolitan Museum of Art in February of 2009, just before her first breakdown at work. Susannah cannot remember going to the museum. She tells the reader that she's hung the postcard above her desk at home, and when she looks at it, she takes comfort knowing that some version of herself went to the museum.
When kept by the buyer, postcards are physical memories and ways to trigger memories of the real art pieces. In the case of Madame X, Susannah only has the physical memento of the painting—not the memory of the painting itself. By adding this layer to the idea of memory and how it functions, Cahalan is able to find peace with the fact that it's impossible for her to remember everything, though these reminders will continue to surface and the process of constructing what happened is ongoing.