The elusive engram: what can infantile amnesia tell us about memory?

Infantile amnesia: forgotten but not gone

“…Clinically, these findings might provide at least a partial explanation for why early life adversity is associated with later anxiety disorders (e.g., McLaughlin et al 2012) as such individuals may explicitly retain their early experiences much longer than normally occurs. Theoretically, these findings may provide a novel approach toward studying the molecular and structural processes involved in memory (e.g., Callaghan et al 2014). That is, animals exposed to early life adversity may exhibit a markedly different developmental profile in the maturation of one, or more, of these processes.…”

“…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.…”

“…In the first phase, the memory is no longer explicitly expressed, but can be recovered if an appropriate reminder treatment is given prior to test. However, if the memory remains in this dormant state (i.e., available but not accessible) long enough, then it may decay sufficiently such that there is no longer a representation of it in the brain (see Callaghan et al 2014, for a consideration of various neural and molecular processes that could be involved in infantile amnesia). In other words, infantile forgetting, and forgetting more generally, could sometimes be due to a retrieval failure and other times to a storage failure; the presence or absence of the physical trace could potentially distinguish between the two cases.…”

“…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 Neuro-Environmental Loop of Plasticity: A Cross-Species Analysis of Parental Effects on Emotion Circuitry Development Following Typical and Adverse Caregiving

“…For example, a growing body of literature has begun to suggest that sensitive periods also occur for emotion development (Callaghan et al, 2014a, b;Callaghan and Richardson, 2014;Gogolla et al, 2009;Tottenham and Sheridan, 2010). In that work, the same molecular and structural signals known to regulate the timing of sensitive period plasticity in the visual cortex, language learning in humans (Werker and Hensch, 2015), and song learning in birds (Balmer et al, 2009) were also shown to regulate the timing of sensitive period plasticity in emotion circuits in humans (see, eg, Callaghan et al, 2014b;Gogolla et al, 2009;Karpova et al, 2011;Nabel and Morishita, 2013). Considering the amygdala-prefrontal cortex is the main neurobiological network underlying emotion regulation, it makes sense to examine whether a sensitive period of plasticity exists in this circuit and, if so, to determine the parameters of such plasticity, including its timing, environmental inputs, and regulators.…”