New insights in human memory interference and consolidation

Learning new facts and skills in succession can be frustrating because no sooner has new knowledge been acquired than its retention is being jeopardized by learning another set of skills or facts. Interference between memories has recently provided important new insights into the neural and psychological systems responsible for memory processing. For example, interference not only occurs between the same types of memories, but can also occur between different types of memories, which has important implications for our understanding of memory organization. Converging evidence has begun to reveal that the brain produces interference independently from other aspects of memory processing, which suggests that interference may have an important but previously overlooked function. A memory's initial susceptibility to interference and subsequent resistance to interference after its acquisition has revealed that memories continue to be processed 'off-line' during consolidation. Recent work has demonstrated that off-line processing is not limited to just the stabilization of a memory, which was once the defining characteristic of consolidation; instead, off-line processing can have a rich diversity of effects, from enhancing performance to making hidden rules explicit. Off-line processing also occurs after memory retrieval when memories are destabilized and then subsequently restabalized during reconsolidation. Studies are beginning to reveal the function of reconsolidation, its mechanistic relationship to consolidation and its potential as a therapeutic target for the modification of memories

From creation to consolidation: a novel framework for memory processing

Long after playing squash, your brain continues to process the events that occurred during the game, thereby improving your game, and more generally, enhancing adaptive behavior. Understanding these mysterious processes may require novel theories

Brain rhythms: enhancing memories

Summary: A new study shows that different processes are responsible for maintaining relevant and suppressing irrelevant information. By promoting the suppression of irrelevant information, memories may be enhanced

Memory processing: the critical role of neuronal replay during sleep

Patterns of neuronal activity present during learning in the hippocampus are replayed during sleep. A new study highlights the functional importance of this neurophysiological phenomenon by showing that neuronal replay is critical for memory processing over a night of sleep

Dual enhancement mechanisms for overnight motor memory consolidation

Our brains are constantly processing past events<sup>1</sup>. These offline processes consolidate memories, leading in the case of motor skill memories to an enhancement in performance between training sessions. A similar magnitude of enhancement develops over a night of sleep following an implicit task, in which a sequence of movements is acquired unintentionally, or following an explicit task, in which the same sequence is acquired intentionally<sup>2</sup>. What remains poorly understood, however, is whether these similar offline improvements are supported by similar circuits, or through distinct circuits. We set out to distinguish between these possibilities by applying transcranial magnetic stimulation over the primary motor cortex (M1) or the inferior parietal lobule (IPL) immediately after learning in either the explicit or implicit task. These brain areas have both been implicated in encoding aspects of a motor sequence and subsequently supporting offline improvements over sleep<sup>3,​4,​5</sup>. Here we show that offline improvements following the explicit task are dependent on a circuit that includes M1 but not IPL. In contrast, offline improvements following the implicit task are dependent on a circuit that includes IPL but not M1. Our work establishes the critical contribution made by M1 and IPL circuits to offline memory processing, and reveals that distinct circuits support similar offline improvements

Exercising control over memory consolidation

Exercise can improve human cognition. A mechanistic connection between exercise and cognition has been revealed in several recent studies. Exercise increases cortical excitability and this in turn leads to enhanced memory consolidation. Together these studies dovetail with our growing understanding of memory consolidation and how it is regulated through changes in motor cortical excitability

Functional imaging: is the resting brain resting?

It is often assumed that the human brain only becomes active to support overt behaviour. A new study challenges this concept by showing that multiple neural circuits are engaged even at rest. We highlight two complementary hypotheses which seek to explain the function of this resting activity

Off-line processing: reciprocal interactions between declarative and procedural memories

The acquisition of declarative (i.e., facts) and procedural (i.e., skills) memories may be supported by independent systems. This same organization may exist, after memory acquisition, when memories are processed off-line during consolidation. Alternatively, memory consolidation may be supported by interactive systems. This latter interactive organization predicts interference between declarative and procedural memories. Here, we show that procedural consolidation, expressed as an off-line motor skill improvement, can be blocked by declarative learning over wake, but not over a night of sleep. The extent of the blockade on procedural consolidation was correlated to participants' declarative word recall. Similarly, in another experiment, the reciprocal relationship was found: declarative consolidation was blocked by procedural learning over wake, but not over a night of sleep. The decrease in declarative recall was correlated to participants' procedural learning. These results challenge the concept of fixed independent memory systems; instead, they suggest a dynamic relationship, modulated by when consolidation takes place, allowing at times for a reciprocal interaction between memory systems

Skill memory: mind the ever-decreasing gap for offline processing

Skills continue to be enhanced even once practice has ceased. Such offline improvements were for a time regarded as the sole preserve of sleep, but recent work shows that they can occur within only a few seconds