Where did I leave those keys?

I had a great idea for a science column for this week, but I forgot it.

I really don't know why I'm so forgetful. As it turns out, most scientists don't know either.

"At the moment, it's still a mystery as to how exactly memory is formed and retrieved," says Maria Natasha Rajah, professor of psychology and head of the brain imaging centre at Quebec's Douglas Institute, one of the top brain research centres in Canada.

Rajah says personal memories, such as where you left your car keys, are the work of the hippocampus, which is a seahorse-shaped structure in the middle of the brain.

When we perceive an event with our senses, it causes neurons in parts of our brains (e.g. the visual cortex) to fire all at once. When that happens, the hippocampus somehow binds these neurons together so they're more likely to trigger as one in the future, creating a memory.

When we recall an event, our frontal lobe somehow gets the hippocampus to trigger the neural network that contains the memory we want.

Why it goes wrong

Norman Brown, a psychology professor at the University of Alberta, says memory happens in three steps – encoding, storage, and retrieval – and can go wrong at each of them.

Encoding is where you create a memory of what you are doing, and actually doesn't happen most of the time, Brown says.

"Our lives are boring," he says, and filled with repetitive actions.

As such, our brains often don't bother to record repetitive details like putting down our car keys, leaving us with literally no idea where we left them, Brown says.

Our brains also have finite capacity and can be distracted by other details and unable to record what we want, Rajah notes.

When it comes to storage, our brains tend to blend similar events together to create generalizations, Brown continues – that's why you can remember your general trip to work but forget the specifics of each trip.

When you want to retrieve a memory, you need to have the right cue to trigger it, Brown says. You might recognize a guy's face, but if you didn't link his name to that face, you won't remember it.

There are a host of other causes for forgetfulness, says Lori Jack, a seniors' nurse who teaches memory enhancement classes for the St. Albert & Sturgeon Primary Care Network.

"One of the biggest factors is sleep," she says, followed by dehydration and poor nutrition. Sickness, medication, menopause and neurological disorders such as Alzheimer's can all muck up our mind's ability to recall information.

Age also seems to play a role, Rajah says. Not only do the hippocampi of seniors shrink, but brain imaging shows that their minds shift modes of operation, becoming more subjective and less likely to record new details. Which happens first – the shrinkage or the mode shift – is one subject of Rajah's research.

Memory boosters

Jack says repetition and mnemonics such as rhymes or songs can all enhance your recall, as can active observation – really paying attention to the details of someone when you learn their name so you can associate more facts with it.

These techniques work because they devote more of our brain's resources to memory formation and crank up our hippocampus, Rajah says.

Brown notes that consciously associating memories with each other also helps, because this raises the number of potential cues you can use to get each one.

There's a big debate on how emotions affect memory, Rajah says. Emotion tends to make events stick in our heads better, but also seems to detract from their details.

"It's hard to remember details of your wedding day," she says as an example – you know it was important, but the details are a blur.

With post-traumatic stress disorder, those details become so blurred that the emotional memory becomes linked to everything, resulting in unwanted recollection.

Good to forget?

Forgetting isn't necessarily a bad thing – Brown goes so far as to call humans "the amnesiac animal." We lose details through generalized memories, but can recall them more efficiently.

And much of what we forget is unimportant, Brown continues.

"Do you really need to remember the muffin you had yesterday?"

The few studies out there on people with near-perfect memory suggest that they are very unhappy, Rajah says. Other research suggests that people with depression tend to remember the world with more accuracy.

"Forgetting painful events is evolutionarily beneficial," Rajah says.

"You need to forget in order to be content."

Now I remember! It was about knots. I'd better get on it.