An average brain weighs just three pounds, but this complex organ contains up to 100 billion neurons.

Each of these tiny cells helps build important information that we call memories.

Jill Price has a gift. Ask her what happened on March 30th, 1981, and she can tell you exactly.

“Reagan was shot, and that was a Monday,” says Jill.

She also has no problem recalling the precise date the Challenger crashed.

“That was Tuesday, the 28th of January, 1986,” she says.

In fact, Jill remembers every detail of her life since she was 14 years old.

“I am completely in the moment, but I also have this split-screen in my head that is always running. It's just random memories always just flowing,” says Jill.

Jill's case raises the questions: why do we remember? And why do we forget?

Neuro-biologist James McGaugh of the University of California says we develop strong memories when we experience an emotional arousal.

“If you are excited, emotionally excited, about something, you're going to remember it better,” says Dr. McGaugh.

When we get excited, the body's adrenal glands release stress hormones that travel through the bloodstream and turn on an area of the brain called the amygdale.

“It's difficult to convey the complexity, the extraordinary complexity, that's sitting between your ears,” says Dr. Gary Lynch, a neuroscientist at the University of California.

But Dr. Lynch has come closer than most scientists. He's captured actual images of memories being formed in animals.

“It's a needle in the needle in the haystack problem, and I think we solved that problem,” he says.

It's a step forward, but there's still so much scientists don't know about memory.

“They just sat there scratching their heads for a long time,” says Jill.

Researchers want to follow Jill throughout her life, hoping to provide answers.

Just because you can't remember something doesn't mean it's not there.

In a recent study, researchers found people had similar activity in their brains when first experiencing an event and trying to recall it.