Bob Petrella can recall any moment from his past. Called highly superior autobiographical memory, there are around 60 known cases around the world. “It’s almost like having a time machine, where I can go back to a certain day or a certain period in my life and almost feel like I’m back there. It’s very visceral.”
Petrella explains that being able to go back to certain times in his life has helped him, like when he was grieving. “It’s very therapeutic to go back to these times and these memories. I feel like I’m still with them in a way.”
For some people, however, the condition is a hinderance, rather than a help. Rebecca Sharrock, an Australian woman with the condition, told BBC Future in 2017: “If I’m remembering an incident that happened when I was three, my emotional response to the situation is like a three-year-old, even though my mind and conscience are like an adult.” This disparity can lead to confusion and anxiety.
For others, it’s a joy. In 2016, Nima Veiseh who also has the condition, told BBC Future it makes him a kinder, more tolerant person. “Some say ‘forgive and forget’, but since forgetting is a luxury I don’t have, I need to learn to genuinely forgive,” he says. “Not just others, but myself as well.”
But how does this happen? One theory is that we all have the same information stored in our minds, we just can’t access it, explains James McGaugh, a professor of neurobiology at University of California, Irvine.
Learn more by watching the video above.
If you liked this story, sign up for the weekly bbc.com features newsletter, called “The Essential List”. A handpicked selection of stories from BBC Future, Culture, Capital, and Travel, delivered to your inbox every Friday.