Minutes after Victorian mother Romy Zunde arrived at a childcare centre to pick up her 22-month-old boy on a hot February afternoon, she made the devastating discovery he was dead in the back seat of her car.

Key points: Mum was sleep deprived and under stress after being sick, inquest hears

Mum was sleep deprived and under stress after being sick, inquest hears Memory limited, cannot discriminate between important, mundane, expert says

Memory limited, cannot discriminate between important, mundane, expert says Boy's body temperature was 40.6 degrees Celsius when found in car

She was severely sleep-deprived, stressed and dealing with a change in routine when she forgot to drop her son Noah at day care in Kyneton that morning, suffering from a phenomenon dubbed "forgotten baby syndrome", an inquest into the boy's death has heard.

Noah succumbed to heatstroke after being left in the car all day. He was one of five children who have died in the past 10 years after being left in cars.

Coroner Sara Hinchey is investigating the possible physiological reasons behind his death in 2015.

Associate Professor of Psychology Matthew Mundy told the hearing he believed it was the result of a catastrophic memory lapse.

"If you are capable of forgetting to post a letter, you are capable of forgetting to take your baby out of the car," he said.

"When you forget something simple like forgetting to post a letter … you assume that that's a simple failure of short term memory, and it absolutely is.

"Your memory is limited, it's limited in the number of things you can remember at any given time and it's limited in the amount of time you can remember a thing for.

"At a neural level, your brain is not discriminating between a letter, your mobile phone or forgetting to retrieve your child from the back of the car.

"Consciously we know that child is way more important than a letter or your mobile phone, but your brain cells … are not making that discrimination for you."

'Perfect storm' in the lead-up to tragedy

Judge Hinchey told the hearing it seemed a "perfect storm of events" had conspired against Ms Zunde on the day of Noah's death.

The court heard Ms Zunde told police she was "really wiped out" and felt like she needed help due to her fatigue on the morning of the tragedy.

She had suffered from gastroentertis earlier in the week, before her young daughter also caught the virus.

Ms Zunde had barely slept in the nights prior to Noah's death and was also dealing with the stress of her pet pigs having been attacked by a dog.

The stress was compounded on the morning of he son's death as she tried to get her daughter to primary school on time and remember the complicated daycare arrangements for her youngest child.

Mum cradled toddler after finding son in car

The inquest heard Noah was normally loud during car trips but unusually fell asleep on the way to day care on the morning he died.

It meant there was nothing to jog Ms Zunde's memory her son was still in the car and, after dropping her daughter at primary school, Ms Zunde's habitual memory took over, resulting in her driving straight home.

When she arrived to collect her son that afternoon, the inquest heard she was confused he wasn't there.

Ms Zunde tried to work out what day it was, initially believing she had turned up to the wrong daycare centre.

She told detectives the car was the last place she expected her son to be.

Ms Zunde opened the back door and finding him inside, cradled him until paramedics arrived. His body temperature was 40.6 degrees.

New car technology available to alert parents

Paramedics were called to 1,907 incidents of children being left in cars last year, with 28 taken to hospital for treatment.

The coroner was told new technology introduced in some cars in the United States alerted parents to the presence of a baby in the backseat when they turn off the ignition.

The device emits a sound and visual cue to remind parents to remove their child.

Associate Professor Mundy recommended similar technology be introduced to new cars in Victoria.

Judge Hinchey will hand down her findings at a later date.