Our earliest childhood memories start from the age of two – far earlier than previously thought.
Scientists have found the area of the brain responsible for memories can be triggered before toddlers even learn to speak.
Researchers had previously thought our earliest memory formed at around the age of three-and-a-half.
The breakthrough may lead to earlier diagnosis of developmental brain disorders such as dyslexia and autism.
Our earliest childhood memories start from the age of two, according to new research. This MRI image shows activity in the hippocampus, a region of the brain associated with memory formation and recall
In the first study of its kind, 22 two-year-olds had their brains scanned using MRI (magnetic resonance imaging) as they slept by researchers at the Centre for Mind and Brain at the University of California, Davis.
The team, led by Professor Simona Ghetti, looked at the hippocampus – a small structure deep in the middle of the brain.
They found the hippocampus was more active when a lullaby the toddler had previously learned was played to them again.
This was regardless of whether the learned song was played as recorded – or played backwards.
However, it was not stimulated by a new one with a different voice, rhythm, tempo and key.
The highest response was observed in those who correctly remembered the place where they learned the song – and a toy associated with it.
The US team said this highlights the role of the hippocampus in the early development of human episodic memory, which is the ability to remember where things happened and what was going on at the time.
Professor Ghetti said: ‘One of the most fascinating questions in psychology and neuroscience pertains to how young children gain the capacity to remember their past.
‘Early hippocampal processes have been implicated in this ability – but a lack of viable methods has hindered assessments of their contribution in early human development.
‘Our results provide direct evidence of a connection between hippocampal function and early memory ability’.
Normally scientists use Functional Magnetic Resonance Imaging (MRI) for measuring activity in the brain.
However, it’s difficult to do this with very young children as the patient has to be able to lie still in a large, noisy scanning machine.
In the first study of its kind, 22 two-year-olds had their brains scanned using MRI (magnetic resonance imaging) as they slept (stock image)
To get around this, researchers used an alternative way which allowed them to look at a child’s brain during nighttime sleep with the MRI scanner
Children first listened to a song while playing with toys in the lab. This meant they formed memories of hearing the song while also playing with a stuffed toy dog.
At their usual bedtime they went to sleep inside the MRI scanner, according to the paper, published in Proceedings of the National Academy of Sciences.
As they slept, researchers played recordings of songs they had heard as well as unfamiliar songs.
Researchers tested the toddlers when they were awake to see if they could remember which room they were in when they heard the song, or if they remembered which toy they played with at the time.
WHAT IS CHILDHOOD AMNESIA?
Childhood amnesia refers to the inability of people to remember events from the early years of their lives.
Researchers believed this was before 3.5 years old. However a new study suggests its likely to be before the age of 2.
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.
Postdoctoral researcher Janani Prabhakar said: ‘Episodic memory – the ability to remember past events along with elements of the spatial and temporal context in which they occurred – is critical for the human experience.
‘It is fundamental to recall one’s unique past, identify what is common across events and make predictions about what the future might bring.
‘This capacity emerges in infancy and undergoes substantial improvement in the first two or three years of life.’
The phenomenon ‘childhood amnesia’ – the inability to remember the first few years of our lives – has been debated by psychologists for more than a century.
When we do try to think back to our earliest memories it’s often unclear whether they are the real thing or just recollections based on photos or stories told to us by others.
But previous research has shown babies as young as six months can form both short and long-term memories that last minutes and weeks, if not months, respectively.
Pre-schoolers, on the other hand, can remember events that go years back.
But it has been questioned if long-term memories at this early age are truly autobiographical.