The Neurobiology of Consolidations, Or, How Stable is the Engram?

Abstract

Consolidation is the progressive postacquisition stabilization of long-term memory. The term is commonly used to refer to two types of processes: synaptic consolidation, which is accomplished within the first minutes to hours after learning and occurs in all memory systems studied so far; and system consolidation, which takes much longer, and in which memories that are initially dependent upon the hippocampus undergo reorganization and may become hippocampal-independent. The textbook account of consolidation is that for any item in memory, consolidation starts and ends just once. Recently, a heated debate has been revitalized on whether this is indeed the case, or, alternatively, whether memories become labile and must undergo some form of renewed consolidation every time they are activated. This debate focuses attention on fundamental issues concerning the nature of the memory trace, its maturation, persistence, retrievability, and modifiability.

Tetris and Word games lead to fewer intrusive memories when applied several days after analogue trauma

“…A recent study stretched the post-trauma intervention to 24 hours post-trauma (James et al, 2015). The authors found that it was still effective, but only if memory was activated 10 minutes before the intervention, consistent with the hypothesis that reconsolidation processes are at stake here (Debiec et al, 2002; Dudai, 2004). This is in line with fear conditioning studies, where propranolol proved to reduce fear responses when administered before memory reactivation (i.e.…”

“…Laboratory interventions have typically been applied during or soon after the analogue trauma, thereby disrupting memory encoding or consolidation, thus hypothesized to disrupt initial acquisition of a memory trace and/or its stabilization (or consolidation) into long-term memory (Dudai, 2004). Memories are malleable during the consolidation phase, which is thought to end after approximately six hours (Nader, 2003; Walker, Brakefield, Hobson, & Stickgold, 2003).…”

“…After retrieval, memories are stored again: re consolidation. Once a memory is reconsolidated, the new trace becomes stable again (Dudai, 2004). Most experiments have targeted memories of analogue trauma in the consolidation phase (for reviews see Holmes & Bourne, 2008; James et al, 2016).…”

Time scales of memory, learning, and plasticity

“…However, right after a new memory is formed, it is still susceptible to perturbations and must be consolidated [e.g. during sleep (Walker et al 2003)] to become stabilized for the next few days (synaptic consolidation; Dudai 2004). The corresponding brain location that is mostly associated with shortterm memory is the hippocampus (Kumaran 2008), where changes in morphology due to synaptic plasticity are found in short-term memory tasks (Shimizu 2000).…”

Retrieval of emotional memories.

“…This has led to controversy about how general the reconsolidation phenomenon is (see Cahill, McGaugh, & Weinberger, 2001;Dudai, 2004Dudai, , 2006, for a full account of this lively debate). Reconsolidation occurs when an organism is trained on a task, and at some time later, the memory trace for this training is reactivated by reexposure either to a stimulus or to the context of the original learning.…”