Why We Don't Remember Early Childhood?

[David Baxter PhD]

Why We Don't Remember Early Childhood?
by Viatcheslav Wlassoff, PhDBrain Blogger
May 23, 2018

Although early experiences are important for personal development and future life, as adults we recall nothing or very little of those early formative events, such as making first steps or learning first words. In fact, when adults are asked about their first memories they usually don’t recall events before the age of 2-3, with only fragmented recollection of events that happened between the age of 3 and 7. This phenomenon is often called childhood or infantile amnesia. It represents an inability of both children and adults to recall episodic memories (i.e., memories for particular events or stimuli that occur in a particular context) from infancy and early childhood, before the age 2-4.

Sigmund Freud was the first researcher to develop the theory of infantile amnesia, as he had observed that his patients rarely had been able to recall memories of events that took place during the first years of life. He believed that childhood memories are being repressed and thus forgotten. Still, modern theories focus on cognitive and social development as an important predictor of childhood amnesia. One possible explanation of childhood amnesia is the lack of neurological development, i.e., the development of brain parts that are in charge of storage and retrieval of episodic memories. For instance, some researchers believe that the development and functioning of the prefrontal cortex (cortex area at the front of the brain) is crucial for the creation of contextualized memories. Moreover, the prefrontal cortex and hippocampus are assumed to be crucial for the development of autobiographical memories. Importantly, these two brain structures develop around the age of 3 or 4.

The lack of neurological maturation, i.e., maturation of brain structures required for creation, storage, and recall of memories during infancy and early childhood might explain the phenomenon of childhood amnesia. According to this explanation, childhood amnesia occurs not due to the loss of memories over time (the forgetting explanation), as Freud had suggested, but rather due to the lack of storing of these memories in the first place. The lack of stored memories, according to this theory, is due to brain immaturity.

Some evidence has suggested that amnesia for events taking place in early childhood (before the age of 2) could be at least partly explained by difficulties with verbally recalling memories that were encoded before language acquisition. In line with this is the fact that the majority of words (the vocabulary) are acquired between the age of 2 years and 6 months and 4 years and 6 months. This is the time period that the earliest memories can be recalled.

Childhood amnesia seems not to be an exclusively human phenomenon. Indeed, some researchers have observed something like infantile amnesia in animals (for instance, rodents). The discovery of amnesia in animals has pointed to the possibility of investigating the underlying mechanisms of childhood amnesia, such as neurological events, by using animal models. The animal studies have addressed the importance of some parts of brain and their development in relation to the childhood amnesia. For instance, they have indicated that high rate of neurogenesis in hippocampus as observed in infancy might explain the accelerated forgetting of contextual fear memories. It seems that integrating of new neurons into the existing circuit might destabilize and weaken the existing memories.

Some researchers believe that it is unclear whether childhood amnesia occurs due to the failure of memory retrieval or failure of their storage. Forgetting might be described as a linear function of the time passing since the event. Since there is a long time span between the early events and recall in adulthood, it might be assumed that early events are simply forgotten. Still, some researchers disagree. This is because they have found that subjects recall far less memories for events occurring between the age of 6 and 7 as would be expected by simply extrapolating the forgetting curve. Thus, forgetting could not completely explain the phenomenon of childhood amnesia. This is why a neurogenic hypothesis of childhood amnesia has been developed.

According to its inventors, a neurogenic hypothesis explains childhood amnesia through the continuous adding of new neurons (neurogenesis) in the hippocampus, as already mentioned above. According to this hypothesis, high levels of postnatal neurogenesis (which occurs in both humans and some animals) in the hippocampus prevents the creation of long-lasting memories. This hypothesis has been experimentally tested in animal models (mouse and rat). The findings emerging from these models have proposed that high levels of neurogenesis jeopardize the formation of long-term memories, possibly by replacement of synapses in pre-existing memory circuits. In addition, the same findings indicate that the decline in hippocampal neurogenesis corresponds with the emerging ability to form stabile memories.

Thus, according to these animal studies, the theory of neurogenesis appears to be a logical explanation for childhood amnesia.

Although the early theory regarding the forgetting or repressing of memories might look like a good explanation of childhood amnesia, more recent findings demonstrate that something else is happening in our brain that contributes to this phenomenon. Whether this is the lack of development in some brain parts, or the continuous synthesis of new neurons, or both, remains to be further investigated. Childhood amnesia cannot be explained by simple forgetting.

References

• Newcombe, N., Drummey, A., Fox, N., Lai, E., Ottinger-Alberts, W. (2000) Remembering Early Childhood: How Much, How, and Why (or Why Not). Current Directions in Psychological Science. 9 (2): 55–58.
• Hayne, H., Jack, F. (2011) Childhood amnesia. Wiley Interdisciplinary Reviews. Cognitive Science. 2(2): 136-145. doi: 10.1002/wcs.107
• Simcock, G., Hayne, H. (2003) Age-related changes in verbal and non-verbal memory during early childhood. Developmental Psychology. 39: 805–814. PMID: 12952395
• Madsen, H.B., Kim, J.H. (2016) Ontogeny of memory: An update on 40 years of work on infantile amnesia. Behavioural Brain Research. 298(Pt A): 4-14. 10.1016/j.bbr.2015.07.030
• Wetzler, S.E., Sweeney, J.A. (1986) Childhood amnesia: An empirical demonstration. In Autobiographical memory (ed. DC Rubin), pp. 191–201. Cambridge University Press, New York, NY.
• Josselyn, S.A., Frankland, P.W. (2012) Infantile amnesia: a neurogenic hypothesis. Learning and Memory. 19(9): 423-433. doi: 10.1101/lm.021311.110

 

[GaryQ]

I pick natural self preservation of sanity!
Seriously, imagine all the people that would need therapy?
how many babies slept in the same room as their parents?
dont think any of us need memories of our parents walking around in their birthday suits and trying (or practicing) to make us a sibling mg:

 

[David Baxter PhD]

Actually, people can remember early traumatic memories but they are probably stored in a different way.

There are two types of memory: episodic memory and semantic memory. Most of our memories are coded semantically, i.e., tagged according to their meaning, which requires language development as described in the first post. But some episodic memories (both traumatic and non-traumatic) are more like a video replay of the original events (not necessarily accurate because all of our memories are subject to distortion). The two types of memory seem to be stored in different parts of the brain and very early memories from prior to the development of the frontal lobe and language would be of the episodic type.

Some of this is theory, of course. This article describes some of the differences, although I think there is more to it than the article covers:

Episodic Memory and Semantic Memory - Types of Memory - The Human Memory

Declarative memory can be further sub-divided into episodic memory and semantic memory.

Episodic memory represents our memory of experiences and specific events in time in a serial form, from which we can reconstruct the actual events that took place at any given point in our lives. It is the memory of autobiographical events (times, places, associated emotions and other contextual knowledge) that can be explicitly stated. Individuals tend to see themselves as actors in these events, and the emotional charge and the entire context surrounding an event is usually part of the memory, not just the bare facts of the event itself.

Semantic memory, on the other hand, is a more structured record of facts, meanings, concepts and knowledge about the external world that we have acquired. It refers to general factual knowledge, shared with others and independent of personal experience and of the spatial/temporal context in which it was acquired. Semantic memories may once have had a personal context, but now stand alone as simple knowledge. It therefore includes such things as types of food, capital cities, social customs, functions of objects, vocabulary, understanding of mathematics, etc. Much of semantic memory is abstract and relational and is associated with the meaning of verbal symbols.

The semantic memory is generally derived from the episodic memory, in that we learn new facts or concepts from our experiences, and the episodic memory is considered to support and underpin semantic memory. A gradual transition from episodic to semantic memory can take place, in which episodic memory reduces its sensitivity and association to particular events, so that the information can be generalized as semantic memory.

Both episodic memory and semantic memory require a similar encoding process. However, semantic memory mainly activates the frontal and temporal cortexes, whereas episodic memory activity is concentrated in the hippocampus, at least initially. Once processed in the hippocampus, episodic memories are then consolidated and stored in the neocortex. The memories of the different elements of a particular event are distributed in the various visual, olfactory and auditory areas of the brain, but they are all connected together by the hippocampus to form an episode, rather than remaining a collection of separate memories.

For example, memories of people’s faces, the taste of the wine, the music that was playing, etc, might all be part of the memory of a particular dinner with friends. By repeatedly reactivating or “playing back” this particular activity pattern in the various regions of the cortex, they become so strongly linked with one another that they no longer need the hippocampus to act as their link, and the memory of the music that was playing that night, for example, can act as an index entry, and may be enough to bring back the entire scene of the dinner party.

Our spatial memory in particular appears to be much more confined to the hippocampus, particularly the right hippocampus, which seems to be able to create a mental map of space, thanks to certain cells called "place cells". Episodic memory does also trigger activity in the temporal lobe, but mainly in order to ensure that these personal memories are not mistaken for real life. This difference in the neurological processing of episodic and semantic memory is illustrated by cases of anterograde amnesia cases (a good example being a case known as “C.L.”) in which episodic memory is almost completely lost while semantic memory is retained.

A further category of declarative memory, referred to as autobiographical memory, is sometimes distinguished, although really it is just one area of episodic memory. Autobiographical memory refers to a memory system consisting of episodes recollected from an individual’s own life, often based on a combination of episodic memory (personal experiences and specific objects, people and events experienced at particular times and places) and semantic memory (general knowledge and facts about the world).

One specific type of autobiographical memory is known as a "flashbulb memory", a highly detailed, exceptionally vivid “snapshot” of a moment or circumstances in which surprising and consequential (or emotionally arousing) news was heard, famous examples being the assassination of John Kennedy, the terrorist bombings on 9/11, etc. Such memories are believed by some to be highly resistant to forgetting, possibly due to the strong emotions that are typically associated with them. However, a number of studies also suggest that flashbulb memories are actually not especially accurate, despite apparently being experienced with great vividness and confidence.

Interdependence of episodic and semantic memory: Evidence from neuropsychology

Tulving's influential theory (Tulving, 1972, 1983, 2001) proposes that human memory can be divided into at least two subtypes. Semantic memory consists of a “mental thesaurus” that provides “the memory necessary for the use of language” (Tulving, 1972 , p. 386), whereas episodic memory consists of memory for “temporally dated episodes or events, and the temporal-spatial relations” among them (Tulving, 1972 , p. 385). Thus, when we state that bicycles are two-wheeled conveyances with pedals and handlebars, we are drawing on semantic memory; when we remember being chased by a dog during yesterday's bike ride around a pond—or even when we remember that “bicycle” was on the second list of words we just read—we are drawing on episodic memory. As this example suggests, the two kinds of memory differ in the kind of conscious experience they involve: episodic memory requires recollection of a prior experience, but semantic memory does not (Tulving, 1985). Although the episodic-semantic distinction has not escaped criticism (McKoon & Ratcliff, 1986; Toth & Hunt, 1999; see Tulving, 2002 , for a response), it has clear heuristic value, and it harks back to similar distinctions that philosophers and psychologists have made since Aristotle (Hermann, 1982; Tulving, 1983).

Neuropsychological investigations have supported this distinction and improved our understanding of each form of memory. Patients with damage to the medial temporal lobes (MTL), for example, have a severe episodic memory impairment that affects both anterograde and retrograde memory: They have little or no ability to acquire new episodic memories, and they have a deficit of premorbid episodic memory that can cover anything from several years (Bayley, Hopkins, & Squire, 2006) to the entire lifespan (Rosenbaum et al., 2008). Moreover, this impairment affects not only the ability to reconstruct the past but also the ability to imagine specific future events (Hassabis, Kumaran, Vann, & Maguire, 2007). At the same time, MTL amnesics’ premorbid semantic memory is largely spared except for knowledge acquired in the immediate premorbid period (Manns, Hopkins, & Squire, 2003). This dissociation provides support for the episodic-semantic distinction and suggests that episodic memory typically relies on MTL structures whereas semantic memories, once consolidated, rely on the neocortex instead.

Additional evidence comes from studies of semantic dementia (SD), a variant of frontotemporal dementia. Patients with SD exhibit progressive neocortical degeneration, particularly in the anterolateral temporal lobe, as well as gradual deterioration of semantic memory. They have difficulty with the verbal identification of stimuli, often giving superordinate names (Hodges, Graham, & Patterson, 1995). The deficit is evident in all modalities that have been tested (including odor and taste; Luzzi, Snowden, Neary, Coccia, Provinciali, & Lambon Ralph, 2007) but may be most severe for verbal material, a finding that has sparked debate about the organization of the semantic store (Simmons & Martin, 2009). By contrast, episodic memory and the MTL, while not normal, are not as severely affected (Chan et al., 2001; Graham & Hodges, 1997). Thus, patients with SD have a broad and severe impairment of semantic memory but relatively unimpaired episodic memory—essentially the complement of the deficit in MTL amnesia.