Developing Intelligence

The Myth of Infantile Amnesia

Freud famously suggested that infantile amnesia is an active suppression of early traumatic memories. However, a review of the modern cognitive literature suggests that at least in some ways, infantile amnesia may actually be a myth.

Perhaps the most intuitive explanation of infantile amnesia is simply that the infant’s brain is not sufficiently developed to support episodic memory. However, substantial evidence argues against this view. For example, the same factors that affect episodic memory in adults also affect infant memory, including age, retention interval, context change, interference, study time, levels of processing, and serial position effects. These factors influence performance on a variety of infant memory tasks, including visual recognition memory, mobile conjugate reinforcement, and the Rovee-Collier train task (although see yesterday’s post for some caveats to this approach.)

Adult-like memories may be formed even in the womb. As reviewed by Hayne, 3-day-old infants were capable of distinguishing a particular passage (from Dr. Seuss’s “Cat in the Hat”) that had been read to them twice daily for the last 6 weeks of gestation from similar passages (matched for word count, length, and prosody). What’s more, these infants preferred the familiar passage even if spoken by someone other than their mother, strongly suggesting that they had encoded (and retained) a relatively high-level representation of the passage’s auditory content.

This and other evidence led Rovee-Collier to argue that both the explicit and implicit memory systems are functional very early in infancy. Therefore, it seems unlikely that infantile amnesia can be explained solely by the immaturity of cognitive memory systems.

But even if these memory systems are functional in a rudimentary sense, it’s still possible that infantile amnesia results from their immaturity. For example, these systems may be highly limited in retention interval. But here again, new evidence suggests that this too is insufficient for explaining infantile amnesia: simple nonverbal reminders of previous experiences seem sufficient for supporting long-term memory in infants. As noted by Hayne, 6-month-old infants can demonstrate memory for a given experience even more than a year later, if simply placed in the same location as the original experience. Similar results have been found with infants as young as 8 weeks of age.

Therefore, infantile amnesia also cannot be explained by an inability to remember over long delays. Infants are likely to encounter numerous reminders of this variety throughout infancy, just a few of which are demonstrably sufficient for supporting long-term memory.

Thus, infantile amnesia cannot be explained solely by neurological immaturity (since both systems appear to be intact) nor by inability to remember over long delays. Instead, this inaccessibility might result from the profound differences between the kinds of retrieval cues used by adults (i.e., verbal cues) and those that would likely be required to retrieve a memory from preverbal infant experience. The alternative “reinstantiation” theory suggests that while infant memories may exist, they cannot be successfully recalled due to the massive synaptic pruning that takes place throughout neocortex in early childhood. In either of these cases, the apparent lack of early-life memory is due to its inaccessibility, rather than an actual failure of retention.

A far more tantalizing conclusion is hinted at by Rovee-Collier, who suggests that “contextual information disappears from memories that have been reactivated once or twice.” Therefore, adult memory may actually contain some early life experiences, but they simply cannot be identified as such due to a lack of source memory.

In summary, there is some reason to believe that the phenomenon of infantile amnesia has been widely mischaracterized. Infants show surprisingly robust long-term memories, and both the explicit and implicit memory systems appear functional very early in life. Based on this evidence, it seems unlikely that retention failure underlies the apparent loss of all early-life experiences. Rather than being completely forgotten, our earliest experiences may actually be mislabeled.

Related Posts:
Overgrowth, Pruning, and Infantile Amnesia
Why Do We Forget Our Childhood? (Cognitive Daily)
Lost Keys: Memory Search Failure

Comments

  1. #1 "Q" the Enchanter
    January 17, 2007

    I would think language development would be highly relevant–not because language constitutes memory, but because (1) language offers an independent mode of thought that can be mnemonically exploited in a distinctive way, and (2) for adults semantic association is a common strategy for memory retrieval tasks (and so presumably would be worthless in retrieving memories acquired before the onset of language).

  2. #2 Katherine Sharpe
    January 17, 2007

    This is fascinating. This idea:

    “that “contextual information disappears from memories that have been reactivated once or twice.”"

    reminds me of another phenomenon: when you have done something many times, it becomes harder to remember any one time (for me anyway; I think it’s probably true for many). I wonder if there’s a similar mechanism at work (something about repetition sponges away the details from a memory).

  3. #3 Allen K.
    January 17, 2007

    What’s more, these infants preferred the familiar passage even if spoken by someone other than their mother, strongly suggesting that they had encoded (and retained) a relatively high-level representation of the passage’s auditory content.

    Spookier still, these (newborn!) infants preferred to listen to unfamiliar passages read by unfamiliar women in their mother’s language rather than passages in other languages.

    For those who are curious about how one determines infant preferences: you give them a pacifier that measures whether they suckle quickly or slowly. First they have to figure out that they can affect what they hear (operant conditioning), and then choose to suck to hear the most familiar sound.

    I read about these (and many other fascinating) studies in “What’s going on in there?”, about brain development from conception – 5 years.

  4. #4 Richard
    January 17, 2007

    Most likely the problem is not that the memories are not there but that they are difficult to trigger. Memories are triggeres when similar associative patters are present.
    Once a person has developed language words can easily trigger memories.
    To trigger infant memories one would have to recrewate similar stimulus as was present when the memory was formed. Since this does not happen very often, infant memories are ‘lost’.

  5. #5 Kenneth Stein
    January 17, 2007

    Given my research, infant amnesia is a consequence of a fundamental paradigm shift that is brought about through interactions with a primary caregiver. I haven’t published on this yet, however you will find related material at Plexav, my blog.

    Summum Bonum.

  6. #6 Kurt
    January 18, 2007

    Fascinating? No, this is horrifying! I’m going to have to really start watching what I say and do around the kiddies from now on. Infantile amnesia is (was) a mighty practical thing to have for less-than-perfect parents.

  7. #7 Joanna
    January 18, 2007

    I don’t know if I’d agree with the mislabelling idea – I seem to agree more with the concept of synaptic pruning. Memory consolidation is much more likely to involve parallel processes, rather than a simple serial STM-LTM paradigm that we hear so often (especially in reconsolidation research).

    The inability to recall most memories from earlier than 3-4 years of age seems most likely to result from the parallel and constant making/unmaking of millions of synapses. As we develop, our brains become less capable of this sort of plasticity – and while infant are capable of quite impressive memory processes, many of the early connections are simply lost as we mature.

  8. #8 Chris Chatham
    January 18, 2007

    Joanna, personally I agree with you. Synaptic pruning just seems like a far more likely explanation (and testable, since we know that there are at least two waves of synapse overproduction + pruning).

    But Rovee-Collier’s suggestion is so tantalizing I had to present it, even though I think it’s unlikely… :)

  9. #9 sarah b
    January 18, 2007

    I have 2 theories: 1)recall is associated with age of linguistic ability. 2)diet has changed in recent human history, specifically choline content mainly in organ meats and eggs (yolks) – there is mounting correlation between choline in prenatal environment and memory later. Very few get the recommended amount through modern diet. I made sure I (ate eggs, etc) the recommended amount of choline when pregnant and nursing.

    Empirically, a couple of weeks ago, just before my son turned 4, I was talking to him about his birth. He asked several questions, then he asked me if they “poked him in the feet”. At first I said “no” then remembered they did blood test, getting samples from the feet. I’m convinced he remembered something about his first hours out.

  10. #10 TealRose
    February 16, 2011

    I am 56 yrs old … and only really found out about childhood amnesia being a reality around, 15 years ago. Up till then .. I honestly thought the people I talked to were either being ‘coy’ and just saying that they couldn’t remember before their first day of school or whatever. This is because I remember back to before my first birthday. [I checked lots of stuff with my mum] I can remember being in my cot, over my mum/dad’s shoulders, wetting etc my nappy, trying to learn how to use a potty! I can remember being in my big pram, and the sound rain made on it’s ‘roof’. I remember the taste of leather as I chewed the leather strap on my reins, drinking from a baby bottle, see my dad dressing for work, the bed they slept in … I remember walking for the first time on my first birthday – and I remember the big bouncy ‘horse’ I had as a gift! I can draw an outline plan of the house I lived in until I was three… etc ! So you can see why I didn’t know about this amnesia phenomena !! I have met one other person in my life who could do this – also a woman [and I believe women do have the edge on early memories]. I can’t remember a time, when I didn’t really HAVE these memories!

    The big thing for me is …WHY do I have the memories and 99% of people don’t ??

    Does anyone else out there have these types of early memories too and does anyone have a theory on US ??

    (Unfortunately, I don’t think I have anyone left alive who can verify all of these memories now … )

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