Role of Sleep in Memory Consolidation

By Maira Ahsan, BScReviewed by Sophia Coveney

Introduction
Sleep
Sleep, Learning and Memory
Memory Consolidation
Role of Sleep in Memory Consolidation
Stages of Sleep and Memory Types
Sleep Deprivation and Memory
Discreet Doubts and Future Research
References
Further Reading

Research undertaken over the last century has revealed that sleep plays a role in the mechanisms directing normal cognitive and developmental processes, including the consolidation of memories. This article will explore the role of sleep in memory consolidation.

Sleep, learning, and memory are all intricate processes that are still poorly understood. Both animal and human research indicate that the amount and quality of sleep significantly affect memory and learning.

This misconception that the brain is "silent" during sleep is based on a fundamental misunderstanding of what happens in the brain during sleep.

Researchers are starting to comprehend the potential impact sleep may have on the cognition of persons with developmental and cognitive deficits. However, it is widely believed that the brain is engaged in active patterns of memory reactivation and reintegration when we sleep.

Sleep

Sleep is described as a temporary condition of diminished receptivity to external stimuli and relative inactivity followed by a loss of awareness and is considered to be a normal and reversible process.

Sleep happens at regular intervals and is homeostatically controlled, meaning that a lack of sleep or a delay in sleep will cause future sleep to be lengthened.

Sleep, learning and memory

The benefits of sleep on learning and memory have been shown to manifest in two unique modalities. As a first point, a lack of sleep makes it difficult to learn anything effectively. Second, sleep is important for learning because it helps consolidate memories.

Although the precise processes behind learning and memory are still a mystery, they are often broken down into three categories known as acquisition, consolidation, and recall.

Acquisition is the process of storing new knowledge in one's memory.  The term "recall" describes the process by which previously stored knowledge may be retrieved (whether consciously or unintentionally).

Memory consolidation

Memory consolidation refers to the stages that occur when a memory becomes permanent.  Proper memory function requires each of these phases; however, acquisition and recall occur only when awake while memory consolidation occurs during sleep by strengthening the brain connections that produce memories.

Researchers believe that unique brainwave properties throughout different phases of sleep are linked to memory development. Consolidation is the process of strengthening and integrating a memory into preexisting knowledge networks by enforcing a stable state on the previously unstable memory trace, which may include numerous waves of short and long-term consolidation processes.

Role of sleep in memory consolidation

During sleep, the brain is at its most conducive to the consolidation processes that integrate newly encoded memory into a long-term store, as opposed to the waking state, when it is suitable to the acute processing of external stimuli, which involves the encoding of new information and memory retrieval.

Due to competition for shared neural resources, encoding and consolidation may be incompatible cognitive processes. Since sleep is characterized by considerably reduced processing of external information, it provides a window of opportunity conducive to memory consolidation.

Numerous studies have shown that interference learning, the injection of norepinephrine and protein synthesis inhibitors or electroconvulsive shocks may successfully impair or increase memory when provided after encoding.

This finding supports the consolidation concept. It is crucial to note that the effects of these interventions are time-dependent and peak soon after learning. Researchers believe that consolidation may occur in waves, with each wave including a separate set of stabilizing mechanisms that follow their own time courses and are dependent on their own underlying neural plasticity processes

Stages of sleep and memory types

Sleep researchers examine learning and memory in two ways. The first method examines how learning new activities affects sleep phases and length. Second, sleep loss impacts learning. 

Different sorts of memories are produced in novel learning circumstances. Scientists are studying whether memory consolidation and sleep phases are related.

Early studies on sleep and memory concentrated on declarative memory or factual knowledge. In one study, intense language students had more rapid-eye movement (REM) sleep. This is when most dreams occur.

Scientists thought that REM sleep aids learning. REM sleep appears to be involved in declarative memory if the material is complicated and emotionally charged, but not if it is simple and neutral.

Slow-wave sleep (SWS) is a kind of deep, restorative sleep that has recently been theorized to serve an important function in declarative memory by digesting and integrating recently learned material. There have been conflicting findings from studies investigating the link between sleep and declarative memory.

Sleep deprivation and memory

Researchers also explore the influence of lack of sleep on learning and memory. Sleep deprivation reduces concentration, attention, and attentiveness, making it harder to acquire information. Without rest, overworked neurons cannot organize information effectively, and we lose access to previously learned knowledge.

Humans may also misinterpret events and exhibit impaired judgment. They cannot make accurate judgments as they cannot effectively appraise the circumstance, prepare, and act.

Chronic weariness impairs performance. Neurons and muscles do not fire effectively, and organ systems are not synced. Sleep deprivation may cause accidents and injuries.

Low-quality sleep and sleep loss affect mood and learning. Mood affects our capacity to learn and recall. Chronic sleep deprivation affects various people in different ways, but a night's rest influences learning and memory.

Discreet doubts and future research

As in every field of ongoing scientific endeavor, there remain unsolved concerns about sleep and memory.  Not all studies agree that sleep helps consolidate memories. In tests where animals navigated a labyrinth, REM sleep increased.

Some experts think the rise in REM sleep reflects the brain's greater demand while learning a new activity. Other studies say any alterations in REM sleep are related to task stress, not learning.

Sleep deprivation's effect on learning and memory is also controversial. After REM sleep deprivation, rats perform poorly in learning activities. This shows that animals need REM sleep to integrate task-related memories.

Thorough experiment-based research on sleep deprivation is essential, and the benefits of sleep should be properly communicated to everyone.

References

• Cappello, K. (2020) The Impact of Sleep on Learning and Memory, Perelman, School of Medicine, Chronobiology and Sleep Institute Blog. Available at: https://www.med.upenn.edu/csi/the-impact-of-sleep-on-learning-and-memory.html  (Accessed: 13 August 2022).
• Carmichael, O. and Lockhart, S. (2012) ‘Neurotrophins and’, Brain Imaging in Behavioral Neuroscience, (November 2011), pp. 289–320. doi.org/10.1007/7854.
• Division of Sleep at Harvard Medical School (2007) Sleep, Learning, and Memory, Healthy Sleep. Available at: https://healthysleep.med.harvard.edu/healthy/matters/benefits-of-sleep/learning-memory (Accessed: 13 August 2022).
• Ellenbogen, J.M., Payne, J.D. and Stickgold, R. (2006) ‘The role of sleep in declarative memory consolidation: passive, permissive, active or none?’, Current Opinion in Neurobiology, 16(6), pp. 716–722. doi.org/10.1016/j.conb.2006.10.006.
• Morris, R.G.M. et al. (2006) ‘Memory Reconsolidation: Sensitivity of Spatial Memory to Inhibition of Protein Synthesis in Dorsal Hippocampus during Encoding and Retrieval’, Neuron, 50(3), pp. 479–489. doi.org/10.1016/j.neuron.2006.04.012.
• Murphy, M. et al. (2009) ‘Source modeling sleep slow waves’, Proceedings of the National Academy of Sciences of the United States of America, 106(5), pp. 1608–1613. doi.org/10.1073/pnas.0807933106.

Further Reading

• All Sleep Content
• What is Sleep?
• Types of Sleep Disorders
• How Can Mindfulness Meditation Improve Sleep?
• Promoting Sounder Sleep in Older Adults