All of us have ever awakened from a terrible night’s sleep feeling groggy, foggy – memories are sketchy, and thoughts drift away. For a long time, scientists have been bothered with the “why” behind this phenomenon. All so much progress has been made toward unraveling the mystery of the real relationship between sleep and memory, yet it still remains a humble yet complex enigma—just one that would prove a key to gaining a much better understanding about memory-related disorders, such as Alzheimer’s and dementia.
At the heart of the current research lies a powerful truth: sleep is not a passive state. It is something dynamic and essential for the consolidation of long-term memories in the brain and maintaining it in the best of conditions. Most recent findings indicate that there appear to be different roles of distinct stages of sleep like REM and slow-wave sleep in processing different types of memory. And while we sleep, another important work is going on in our brain: flushing out toxins, which, if not quickly cleared, might cause mental degradation. Researchers from Yale are among those who study the intriguing relationship of sleep with memory and found out how, for instance, our brain converts the fleeting moments into a lasting memory.
How Episodic Memories Are Formed and Evolved
Episodic memories, or the memories associated with specific events in our lives, form and evolve by a long, step-by-step process. According to Dr. George Dragoi of Yale University, “episodic memories are confederated within our semantic memories, or just general facts about the world.” To learn more about episodic memory, visit this article on episodic memory. Episodic memories are highly dependent on the hippocampus; that is, the hub of the brain’s memories. They are also largely dependent on the neocortex. These two areas are indeed interactive at two crucial stages: encoding and consolidation.
Stage 1: Encoding Memory
Encoding is kinda like taking a picture of everything going on in the world around you. In this stage, the brain rapidly takes in outside stimuli and encodes these outside stimuli as sequences within the hippocampus. These sequences serve as placeholders for the memory, almost like filing away the key aspects of an event. According to Dr. Dragoi, when these neurons are activated, they fire one after another to create a linked chain of memory. The amygdala, on the other hand, will “tag” certain memories with an emotional charge—these could be negative, positive, or nostalgic.
Phase 2: Consolidation of Memory
After encoding, the brain goes into consolidation mode. This process is crucial because only when asleep can the encoded memories become solid. During this process, the slow-wave sleeps particularly harden the encoded memory. These sequences are consolidated by the brain into its greater network of knowledge, where they are stabilized for long-term storage in the neocortex. According to Dr. Dragoi, this step would be impossible without consolidation. The memory encoded would disappear into nothingness, leaving little behind. “Encoding is necessary, but it’s not enough on its own,” Dragoi explains. “Consolidation during sleep ensures that you retain what you’ve learned.”
Sleep as a Memory Consolidator
What is the rationale for why sleep is such a good consolidation state for memory? One idea is that sleep creates an environment that essentially flushes out all of the external stimuli and has the brain focus inward on housekeeping. All the neurotransmitters that facilitate communication between the hippocampus and neocortex are plentiful during sleep; thus, these are excellent conditions for the integration of memories.
But there’s another very important thing about sleep—the ability to prune neural connections in the brain. The brain prunes away unnecessary links or weakened neural links just like a gardener might prune an overgrown tree to encourage growth of the overall plant. Through sleep, it deletes excess neural links for it to provide space for new memories. According to Dr. Dragoi, in adults, the connectivity structure of the brain is established, but their strength varies with time. In other words, “Sleeping allows the brain to fine-tune or do plasticity on these connections, so it gets into homeostatic balance.”
Research Highlight: Sleep improves the synthesis of protein templates necessary for synaptic functions in the brain. Without sleep, such templates never come to fulfill their functions, making a more profound biochemical relationship between sleep and cognitive health.
Cleaning Out the Brain’s Waste: The Cleaning Crew Sleeping Breathes
Recent studies now prove that the brain has a detoxifying process during sleep: it removes toxins created throughout the day. Advanced imaging techniques, spearheaded by Dr. Helene Benveniste and her research team, unveiled how sleep clears out pathogenic metabolites that are accrued daily. Included in this list are beta-amyloid and tau proteins, known to be harmful when not checked at increased risk for causing Alzheimer’s.
Benveniste draws an analogy for the process—a nightly cleanup session where the brain uses the glymphatic system to wash off its toxins. This system is like the body’s lymphatic system but works within the brain itself, allowing cerebrospinal fluid to flow through channels to sweep away waste and keep the tissues of the brain healthy. Evidence from these studies shows that this system functions optimally only at deep sleep, providing another mechanism by which quality sleep is required for long-term brain health.
Sleep Quality and Alzheimer’s Disease: A Very Dire Connection
Several researches have confirmed that sleep deprivation poses a serious threat to the health of the brain. One study has established that even a night of poor sleeping can increase the accumulation of beta-amyloid within the hippocampus, a brain region tasked with memory. All these findings ring an alarm in respect to long-term effects that may result from chronic sleep deprivation, especially in respect to cognitive disorders such as Alzheimer’s disease. Dr. Benveniste’s work underlines the protection of the glymphatic system, since it may be even lowering the load of detrimental proteins.
An interesting finding from her research is that some aspects such as sleeping position influence the efficiency of the glymphatic system. Sleeping on one’s side or back maximizes the system’s capacity to clean the body’s waste, which has huge implications for how we consider sleep as the protector against cognitive decline.
Tapping into the Power of Sleep to Enhance Cognitive Wellness
As sleep in relation to memory is deepened more, researchers are looking for ways of tapping into sleep for the enhancement of cognition. One researcher and activist is Dr. Hilary Blumberg, who investigates and explores how sleep interventions improve emotional regulation as well as memory in older women. Her activity is done through work in social rhythm therapy, also known as SLEEP-SMART, helping those individuals to regularize their sleep and daily activities for healthier cognitive aging. Simple practices like morning sun, upkeep of a regimen of meals, and not staring at electronic displays before bed may significantly influence memory and mental well-being.
The Way Forward: Sleep’s Larger Role in Neuroscience
Although we have greatly advanced in uncovering what sleep does to promote memory function, much remains to be unraveled. Ongoing researches, such as those by Dr. Dragoi and Dr. Benveniste, are still prying into the deeper mechanisms underlying sleep effects on the brain. Indeed, as research advances, it will hopefully reveal not only a deeper understanding of sleep in relation to cognitive health but also new therapeutic strategies for prevention or mitigation of memory disorders. Well, sleep seems to be more than just a time to rest—it’s actually one of those important processes that shape us up on how to remember, learn, and grow.
