Infantile amnesia: Early fogging in the brain

21. July 2014
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Memories of earliest childhood experiences reach back only as far as the age of three to five years. The maturation of the nerve centres is a neurological explanation for the fact that the time period before this "disappears". However the cultural sphere also determines the extent of infantile amnesia.

“Do you remember when you weren’t able to decide between Teddy and picture book?” Most people would answer this question with “No”. Even when this difficult decision at that time in life as an infant had fundamental importance.

Time blanked out

With increasing age, we forget more and more of what fills the experience treasure-box of our lives. According to the findings of Douwe Draaisma of the University of Groningen, more than 70 percent of our mental flashback memories relates to the first third of our existence. Aligned to this, life seems to pass by faster and faster, with fewer and fewer significant events. And yet the span covering the first three to five years remains almost completely blanked out from our mind. “Infantile amnesia” is the term that Sigmund Freud coined when he described this phenomenon of early-year memory blankout. This lack of time memory is not merely a human phenomenon. It can be studied just the same with mice and rats.

Memory capacity already present shortly after birth

The brain of infants can already store experiences and also retrieve them as needed. Infants whose mothers had over the pregnancy period regularly watched television programs with characteristic signature tunes are able to be calmed using these melodies – perhaps remembering a wonderfully peaceful time before postnatal stress. The child can actively recall impressions and experiences, however, only from the age of two years onward. The stuffed toys that the mother had hidden in one of many drawers of a chest can be later retrieved by many children very early in life. Mark Howe of the City University in London was able to show in studies that the requirement for this memory is the “cognitive self”, the knowledge of one’s own personality and experiences. A characteristic symptom of this: children recognising themselves in the mirror.

From the age of four to five years, adolescents are able to put their memories into words; at seven they produce their first stories about past childhood experiences. At this age, as Patricia Bauer of America’s Emory University in Atlanta found out, significantly more memories from early childhood are still present than are for example at nine years of age. Discussions on common significant experiences between the mother and the child which occurred when the child was three years old are still still preserved with seven-year-olds up to around 60 percent, two years later however this figure is no more than 35 percent and even then only in exceptional cases. The younger the child, the faster and more intense the forgetting process – Bauer describes the dynamics involved in infantile amnesia as such. At best memory builds up in attachment to events in which the parent-child conversation was very intense – or is associated with strong emotions.

Variable degree of amnesia

This “memory limit” recalling early childhood is apparently independent of age and lifespan, something which has been increasing over recent generations. Respective reports from about a hundred years ago state very similar figures in relation to infantile amnesia to those from the 21st century. But there are also differences: the experience memory bank of first-borns goes further back than those of their siblings, the same is true for women who better remember the period of time before kindergarten than do men. However, culture and the environment seem to have an equally important influence on the forgetting process. Thus in Europeans the phase of the “forgotten years” runs up to about three and a half years, with East Asians it goes on up until the age of six. The natives of New Zealand, the Maori, however can still retrieve experiences from the age of 2.5 years from out of their memory drawer.

Communication training for remembering

Perhaps, speculate amnesia experts, this is related to narrative culture between mother and child during the first years of life. Europeans and North Americans discuss common experiences in greater detail than do the Chinese. With the Maori, stories and storytelling about the family and about their past belong to their traditions. Already more than ten years ago Qi Wang from Cornell University found not only that the memory of Americans goes back further than that of the Chinese, but that his U.S. colleagues also knew more details from that time than do people over the other side of the Pacific. Whoever as a mother includes intensive discussion with the toddler as part of child-raising also ensures that the offspring much better remember their childhood later than do the offspring of more taciturn parents – a piece of information obtained by Patricia Bauer’s working group.

New nerves provide for memory oblivion

The neurological processes that lead to forgetting of early childhood remain still partly unclear. However, it does appears that neurogenesis in the area of the hippocampus plays an important role. The region is considered to be the seat of long-term memory. The gyrus dentatus, a portion of the hippocampus, matures only at four to five years of age. Without it, memories cannot shift across into long-term memory. A few weeks ago an article, produced by Paul Frankland and Sheena Josselyn’s working group at the University of Toronto, making clear how the “forgetting” may be happening, appeared in Science magazine. According to the article, the information stored is no longer available due to a “remodelling process”, that is the insertion of new neurons in the hippocampus area. As the researchers increased neurogenesis in mice, they became automatically “more forgetful”. Conversely, their memories stayed awake longer when the formation of new nerve decreased.

With guinea pigs and bush rats (degus) most of the granular cells of the hippocampus are already formed before birth. With the nest leavers hardly any more de-novo synthesis of neurons occurs. Their memory processes are much better than those of the nest dwellers. However, if one stimulates nerve regeneration in these animals, the forgetfulness of early childhood also sets in.

No memory without feelings

Whether the stored memories are completely lost or just very difficult to access has not been determined yet. What seems very important in the storage of memories alongside an association with strong feelings is the link to the amyygdala, or the “feeling centre”. Neuroscientist Wolf Singer of the University of Frankfurt says that memories are only possible in the context of emotion; an “objective remembering” does not exist. If the connections between the hippocampus and the amygdala are broken, the memories are wiped out.

Is data recovery possible?

Can memories of events during early childhood be retrieved and brought out in detail? And if so, how? This question not only interests neurologists and psychologists, but also for instance lawyers and judges in legal processes in which crimes are supposed to be re-examined many years later, and in which a child was a witness or an affected party. How reliable the stored data impressions are and whether they are subject to manipulation is a topic that is being intensively researched. The knowledge about the processes in infantile amnesia could nonetheless also be used by adults who just want to forget trauma events, whether in childhood or later in life. And the clearer it becomes why and how we delete events in our early life from our minds, perhaps the chance also rises of learning to at least slow down the forgetfulness which arises in the second half of life.

 

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Medicine, Neurology, Psychiatry

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I have memories of people speaking to me, and I was unable to talk back to them. My mother said that I was less than 2 years old in the house that I have these memories.

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