Why you can't remember your earliest memories: It's your brain's way of growing neurons and means you remember for longer as an adult
- During childhood, brains are more limber which means they absorb information
- However, parts of the brains that retain information are still under construction
- Memories made during this period are likely to become inaccessible as adults
- This is because the brain is changing and new neurons grow in the hippocampus
From getting lost in the supermarket to going on the rocking horse at playschool, memories from before the age of five are few and far between for most people.
This is due to 'childhood amnesia', which refers to the inability of people to remember anything from before the age of of around three and a half.
During childhood, brains are more limber, which means they are able to absorb lots of information in a small space of time.
However, parts of the brains that retain this information are still under construction, scientists say.
From birth until our early teens, essential circuitry in the brain is still being laid down, as electric pathways become lined with fatty tissues to become more conductive, meaning we are able to retain these memories.
In the process, memories from our 'limber' childhood brain are likely to become inaccessible as our neurons are restructured in the formation of our adult brains.
From getting lost in the supermarket to going on the rocking horse at playschool, memories from before the age of five are few and far between for most people (stock image).
'This is a phenomenon of longstanding focus,' Patricia Bauer of Emory University, a leading expert on memory development told Nautilus as part of an in-depth feature.
It was previously thought children were unable to retain memories before the age of seven.
However, in 2005 researchers found five and a half year olds remembered 80 per cent of things that happened when they were three. By the time they reached seven and a half they remembered less than 40 per cent.
This shows children can remember things, but that these memories start to fade.
In the past few years, scientists have been finding out about the biological basis for this memory loss.
Throughout childhood the brain is laying down circuitry and lining key pathways with fatty tissue. During this period of growth, new bridges are created between neurons.
According to experiments by Paul Frankland, a neuroscientist at the Hospital for Sick Children in Toronto, the growth of new neurons in the hippocampus is essential for remembering and forgetting.
Not only do these parts of the brain degrade, they also become concealed as we age.
Dr Frankland and his wife Josselyn carried out research on adult and infant mice kept in cages - one cage was the size of a shoe box and the other much larger.
The mice were given mild electric shocks when placed in the larger cage.
The older mice stiffened with fear when they were put in it, in anticipation of the shock, while the young mice forgot about it in the space of a day.
However, when the adult mice ran on hamster wheels after their shock they forgot their pain.
This is because it stimulated the growth and development of nervous tissue - a process called neurogenesis.
WHAT IS CHILDHOOD AMNESIA?
Childhood amnesia refers to the inability of people to remember events from the early years of their lives - typically before 3.5 years old.
Females appear to to have better memories for this than men and on average could go back further than men.
There a number of theories about why this might be happening.
The most controversial was put forward by psychoanalyst Sigmund Freud who believed it was a response to sexual repression.
Females appear to to have better memories for this than men and on average could go back further than men (stock image)
Another theory suggests childhood amnesia is down to a lack of lack of language skills before the age of three.
It was previously thought children were unable to retain memories before the age of seven.
However, in 2005 researchers found five and a half year olds remembered 80 per cent of things that happened when they were three.
By the time they reached seven and a half they remembered less than 40 per cent.
This shows children can remember things but that they don't last for as long as things that happen in adulthood. When researchers gave the mice specific drugs that hindered neurogenesis the young animals were able to remember things better.
By inserting a fluorescent protein into the DNA of the mice's brain they found neurogenesis did not wipe out memories, but restructured them so much the original memories were harder to recall.
In humans experts believe the same thing is happening.
'We think it's an accessibility issue, but it's sort of a semantic issue too', said Dr Frankland.
'If a memory becomes impossible to access, then it is effectively erased.'
Due to these cycles of growth and decay, any memories that do survive childhood are likely to be blends of genuine recollections and things that we've heard or dreamt up.
Memories made during this period are likely to become inaccessible as the brain changes and new neurons grow in the hippocampus (stock image)
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