Infantile amnesia: A neurogenic hypothesis

Abstract

In the late 19th Century, Sigmund Freud described the phenomenon in which people are unable to recall events from early childhood as infantile amnesia. Although universally observed, infantile amnesia is a paradox; adults have surprisingly few memories of early childhood despite the seemingly exuberant learning capacity of young children. How can these findings be reconciled? The mechanisms underlying this form of amnesia are the subject of much debate. Psychological/cognitive theories assert that the ability to maintain detailed, declarative-like memories in the long term correlates with the development of language, theory of mind, and/or sense of "self." However, the finding that experimental animals also show infantile amnesia suggests that this phenomenon cannot be explained fully in purely human terms. Biological explanations of infantile amnesia suggest that protracted postnatal development of key brain regions important for memory interferes with stable long-term memory storage, yet they do not clearly specify which particular aspects of brain maturation are causally related to infantile amnesia. Here, we propose a hypothesis of infantile amnesia that focuses on one specific aspect of postnatal brain development-the continued addition of new neurons to the hippocampus. Infants (humans, nonhuman primates, and rodents) exhibit high levels of hippocampal neurogenesis and an inability to form lasting memories. Interestingly, the decline of postnatal neurogenesis levels corresponds to the emergence of the ability to form stable long-term memory. We propose that high neurogenesis levels negatively regulate the ability to form enduring memories, most likely by replacing synaptic connections in preexisting hippocampal memory circuits.

Adult neurogenesis in the mammalian hippocampus: Why the dentate gyrus?

“…Related to longer-term memory processing Josselyn and Frankland (2012) have proposed that neurogenesis may actively destabilize memories and hence promote forgetting. The authors cite the inverse correlation, through development, between rates of hippocampal neurogenesis and the ability to lay down longterm memories, and have found that promoting AHN postlearning diminishes the retrieval of previously established memories (Frankland et al 2013).…”

Infantile amnesia: forgotten but not gone

“…As one example, in a series of experiments Rovee-Collier and colleagues have shown that retention in human infants trained on an operant procedure (e.g., the mobile conjugate reinforcement task, where the infant learns to kick one leg to produce movement in an overhanging mobile, or the train task, where the infant learns to press a manipulandum to cause an electric train to move) increases monotonically with age over the first years of life (for review, Although we have long been aware of the robust phenomenon of infantile amnesia, in the past 50 years there have been surprisingly few advances in our understanding of the physiological bases of this rapid forgetting. However, several recent papers have suggested potential molecular and structural mechanisms that could be involved in infantile amnesia (e.g., Josselyn and Frankland 2012;Frankland et al 2013;Callaghan et al 2014). These potential mechanisms are largely derived from recent studies on the molecular and structural bases of memory in adults.…”

“…However, several recent papers have suggested potential molecular and structural mechanisms that could be involved in infantile amnesia (e.g., Josselyn and Frankland 2012;Frankland et al 2013;Callaghan et al 2014). These potential mechanisms are largely derived from recent studies on the molecular and structural bases of memory in adults.…”

The NICHD Protocol: Guide to Follow Recommended Investigative Interview Practices at the Barnahus?

“…Empirical studies have shown that events, including traumatic ones that occur before the age of 2-3 years are unlikely to be available for conscious verbal recall (Cordon et al 2004;Newcombe et al 2007;Simcock and Hayne 2002). This phenomenon is usually referred to as "infantile amnesia" and has been validated by over a century of empirical research (Bauer 2007;Josselyn and Frankland 2012). By the age of three, however, children's recall of stressful events can be consistent and robust (Peterson and Warren 2009), and they are able to recall stressful negative events over time, as well as reporting new correct information (Baugerud et al 2014;Lamb et al 2011).…”