A three-year-old girl in Edmonton died on Tuesday after being left alone inside a sweltering car. On Wednesday, a funeral was held for a toddler in Milton, Ont., who died the week before after also being left alone in a car.

The question that is asked following such tragedies is always the same. How could anyone forget a child in a car?

The answer, terrifying and surely for many people hard to accept, is that this could happen to anyone.

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"Memory is a machine, and it is not flawless. Our conscious mind prioritizes things by importance, but on a cellular level, our memory does not. If you're capable of forgetting your cellphone, you are potentially capable of forgetting your child," David Diamond, a professor of molecular physiology at the University of South Florida, told the Washington Post in 2009.

Stress, he explained, can weaken the parts of the brain responsible for higher functions, leaving us on a sort of autopilot operated by the basal ganglia, a part of the brain casually referred to as the "reptilian brain."

"The important factors that keep showing up involve a combination of stress, emotion, lack of sleep and change in routine, where the basal ganglia is trying to do what it's supposed to do, and the conscious mind is too weak to resist," Diamond said.

As the Washington Post story explained, there is no consistent profile of people who have left children in cars to die. It happens to the absentminded but also to task-oriented A-types. It happens to the wealthy and it happens to the poor.

Sometimes, of course, there is a history of neglect, or the parents knowingly left the child in the car. But very often it is an otherwise loving, attentive parent who forgets a child is still in the vehicle.

"Some people think, 'Okay, I can see forgetting a child for two minutes, but not eight hours.' What they don't understand is that the parent in his or her mind has dropped off the baby at daycare and thinks the baby is happy and well taken care of. Once that's in your brain, there is no reason to worry or check on the baby for the rest of the day," Janette Fennell, who runs the Kansas City-based non-profit organization Kids and Cars, told the Washington Post.

So far this year, 13 children have died in the United States after being left alone in vehicles, as The Globe's Vidya Kauri reported on Wednesday.

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There are 37 heat-stroke-related deaths of children in vehicles each year in the U.S., while in Canada where statistics are not kept, there are an estimated four to six such deaths annually, according to the report.

"It's not malicious. People get busy, and sometimes they are out of the routine," Raynald Marchand, the general manager of the Canada Safety Council, told The Globe.

He suggested parents or anyone else driving the car leave something in the back seat – a brief case, a purse – that will remind them that a child is there, no matter what else might be on their mind.

Charges are rarely laid in cases where a child dies after being left unattended in car, he added.

"If the child dies, quite often [police] go, 'They've already had the optimum punishment. How can we punish them any more than this?' "