Infantile amnesia

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society. Autobiographical episodes, so it is suggested, become encoded properly only after the infant becomes aware of the social function of autobiographical memory, which is postulated to be, according to this view, the development of a life history that can be shared with others (Nelson 1993).

Many of the aforementioned explanations are not mutually exclusive. Immature brain circuits in infancy, such as frontal "cortex and cortico"limbic circuits, may be yet unable to subserve the cognitive and the psychosocial faculties of categorization, 'inner language', self-comprehension, or social understanding. All this does not imply that very young infants do not have the ability to acquire ad-hoc declarative knowledge (they

do; Rovee-Collier 1997), or that their brain is incapable of amazing feats of learning and memory (it does; Saffran et al. 1996; Jusczyk and Aohne 1997). Even fetuses may have learning and memory capabilities that parents-to-be commonly disregard (Hepper 1996). In estimating the mental capacity of infants, it took a lot of grant money to reach the conclusion reached by every normal parent: these babies outperform us in many ways.

So, regardless of the exact mechanism, what could be the phylogenetic and ontogenetic rationales for preventing adults from remembering their adventures in the crib? It might be related to a mix of biological constraints and selective pressures. First, evolution did not come up (yet?) with the ability to construct instantly a perfect brain; it takes years to "develop. Second, slow brain maturation may have an advantage in coping with a changing environment, as it reduces the chance of fast and robust encoding of erroneous outcomes of certain types of learning in early infancy. Third, autobiographical memory could lack significant phylogenetic advantage early in life (and see "capacity). All the above combined, it probably pays better to dedicate first the brain power of the newborn to the acquisition of critical, basic "skills, rather than to the long-term declarative memory of the pains and the joys of the first months of life.

Selected associations: Amnesia, Development, Episodic memory, Persistence, Real-life memory

1The frontal cortex can suppress unwanted memories (Anderson and Green 2001), but there is no evidence that this is involved in infantile

10 13 Years since event

Fig. 36 Although the existence of infantile amnesia is supported by introspection, personal accounts, and anecdotal evidence, its objective verification under *controlled conditions is not trivial. Three major types of variables are involved in such experiments: the age at learning, the age at retrieval, and the length of the retention interval. The ideal experiment should control the age at retrieval, vary the age of learning, and, most importantly, define the expected normal forgetting over the retention interval. Infantile amnesia will then become apparent as accelerated forgetting below a certain early age at learning. The graph depicts the hypothetical distribution of memories across the lifetime of a 20-year-old human *subject. The solid line represents an ideal function of normal forgetting, while the inflected broken line represents the accelerated forgetting that one should observe in infantile amnesia. Based on the analysis of the data in the scientific literature, Wetzler and Sweeney (1986) confirmed that indeed, phenomena that approximate the hypothetical curve are observed in reality, and that there is accelerated forgetting for memories acquired below the age of 5. (Adopted from Wetzler and Sweeney 1986.)

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