People with HSAM have brains that are different from most everyone else’s. There’s a part in their brain called the temporal lobe that’s bigger. Which makes sense, since the temporal lobe is where we store memories. They say they can find the cure for Alzheimer’s by studying people who have HSAM. They hope to reverse engineer the process of how these kinds of memories work so they can prevent memory disorders and maybe even cure them.

Today at the mall my brain showed a glimpse of what it can do, of what it’s been hinting at for a while. I used to think I might have an eidetic memory or a photographic memory, but I’ve ruled that out after this afternoon. After scouring the Internet, I’m pretty sure I have what’s known as a highly superior autobiographical memory.

There’s a doctor who studies people with HSAM. He says people with this kind of memory can recall almost every day of their lives in amazing detail, as well as public events that hold personal meaning to them. They can “see” a vivid picture of each day in their heads.

I test myself by looking at old class pictures from three years ago. Now that I’ve stopped trying to ignore it, my memory clicks on quickly. Where I saw the map earlier, a 3-D calendar pops up in the air in front of me. I can “see” pictures on each of the dates—little clues about what happened that day.

Click. I pick a calendar square, pulling it out and opening it up. It unravels, with each detail playing out in front of me. I’m back in the classroom, with the faint smell of Mr. Guerro’s cologne mixing with the musty aroma of our class’s pet guinea pig, Marbles. I remember what each of my friends was wearing that day, down to their shoes and backpacks.

I immediately know why this particular day stands out. It was right after Clay was born, when Mom went from sad to never getting out of bed.

I felt alone at home. I didn’t want to be alone at school, too.

So I tried extra hard to fit in and be liked. I smiled more, laughed at jokes even if they weren’t funny. And, of course, I copied how the most popular girl in class dressed. On this day my green sweater exactly matched one Piper wore the previous year.

Piper almost never wore something twice. But that day she did.

“Look, Piper!” Megan said with a smile that was a little too wide. “You and Lulu are wearing the same thing.”

“I bought it last weekend,” I said.

“So did I,” Piper said with a forced laugh, her glare fixed and present. She slung her arm across my shoulder and posed with her head next to mine. “Who wore it best?”