Researchers believe they are closer to discovering why adults cannot remember the first few years of childhood, after a study found the increased rate that new cells are produced at in the brains of babies could increase forgetfulness.

Scientists from the University of Toronto in Canada found that 'infantile amnesia', or the inability to recall memories from early childhood, could be exacerbated by the higher rate the human brain generates new cells at in early life.

Their study found that the increased rate of formation of new cells could be pushing out established memory circuits, Science Alert has reported.

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Infants are constantly learning new things resulting in lots of activity within the hippocampus region, which is associated with learning and memory.

During the study, the team produced memories in rodents by creating an association between a place and a mild electric shock.

They then increased or decreased the rates of neurogenesis to see what would happen to the memories later on, according to Vox, using a running wheel or drugs.

Boosting the rate of neurogenesis, the process of the brain making new cells, in rodents increased forgetfulness, whereas rodents that had the process slowed down were instead better at remembering things.

They also found the same results in guinea pigs and degu, who have naturally lower rates of neurogensis as infants because they are born with more mature brains. When the team increased their rate of neurogenesis, they struggled to store memories from shortly after being born.

Mazen Kheirbek, who studies the birth of new brain cells at Columbia University said: "I think [the new hypothesis] provides a very compelling mechanism for why we don't remember infantile memories."

However, he suggested the forgetfulness could also be attributed to an increased ability to learn new things, adding: "So there is a tradeoff there, preserving the older memories may come at the cost of making new ones."