The Unique Coupling of Sleep and Memory
We basically incorporate the knowledge we accumulate from our daily experiences, then integrate them during the period of sleep when our brain waves reach their slowest frequency. This period is known as the delta sleep stage. Wouldn’t it be incredible if we could somehow use this information to optimize memory?
Researchers recently studied brain circuitry during deep sleep when this memory processing occurs. The intent was to look for ways to prevent memory loss and enhance memory retention in mice.
They specifically studied the touch perception of certain textures and followed the brain pathway associating the touch perception with the memory associated with the texture. The researcher postulated that the same pathway involved in creating this “texture memory” can be _reactivated_and associated with the same experience, so that one can learn more in the future, expanding on this prior memory.
This pathway they identified, called the “top down cortical pathway,” is the pathway that is responsible for memory consolidation.
One way to make sure you are consolidating memories during sleep is to make sure you get deep, refreshing, undisturbed sleep. If that doesn’t happen, you can typically suffer with memory lapses or poorly integrated memories. The importance of this research, which clearly identifies this pathway, is that it has the potential to be manipulated in order to reactivate sleep-deprived neurons so that memory is enhanced.
It’s clear that having memories of previous experiences is crucial for adaptation to one’s environment and survival. When inspecting memory function more closely, it has three important and distinct phases: encoding, consolidation and retrieval.
During the encoding process the experience you have is followed by a memory trace. This memory trace can often be mixed with different influences and this results in decay or forgetting of the memory of the real experience. More on this in a moment. It is during** consolidationthat this memory trace is _stabilized_so it can be integrated into pre-existing similar memories. Finally, during retrieva** l, the stored memory is accessed and recalled.
It is the waking brain that processes new experiences and encodes the new information into what is known as a memory trace. As I mentioned, there are two phenomena that can influence the strength and integrity of the memory trace: Decay, which allows this trace to be forgotten over time and** interference** which results from conflicting previous information that the brain already holds and is in conflict with the new memory. These two influences will weaken this memory trace.
When the brain is in sleep mode, there is reduced external information, creating optimal conditions for the consolidation process and for long-term memory of an event or events to be established.Studies have shown that some memory traces are not consolidated once but rather can be reactivated by a reminder or by active retrieval (you trying to remember it) which allows for reconsolidation. In this case the memory is strengthened further and will likely persist as a long-term memory. If you think about it, some memories are quite strong, while other memories may fade or were never captured well.
Creating and retaining memories is even more complicated. Different parts of the brain can actually be involved in the process of memory and certain aspects of consolidation may actually occur in different phases of sleep.
There is also declarative memory, which is the knowledge of fact-based information (different from experiences). This learned information is more apt to be entered during slow wave delta sleep where single items are processed individually. This brain activity is done with purpose, like studying for an exam. It’s well known that “pulling an all-nighter” before an exam makes it more likely that less of the learned information will be retained and more will likely be forgotten.
Lastly, there is procedural memory, which is remembering how to do something (based on having done it previously). This requires a more complex pattern. The consolidation for this memory takes place during REM, where previous experiences are matched up during dreams. This allows one the feeling of the experience so it can be repeated without even thinking about it (like riding a bike). Lighter phases of sleep also play a role in** motor learning****,** while** visual learning** depends on consolidation during lighter and deeper phases of sleep. The result is that all phases of sleep are needed in order to incorporate procedural memory, which involves motor, cognitive, and visual functions.
Much of the knowledge we currently have regarding memory was gained from studies that examined sleep deprivation and selective sleep deprivation (loss of certain phases of sleep).
If you think about it, humans have to learn and remember more complex and a greater variety of tasks than any other species. Our memories are all learned and consolidated, not only during sleep but also while awake. In fact, studies show that recall of facts learned right before sleep is greater than recall of the same material learned a whole day before sleep. You can actually test that theory out the next time you need to remember some very important information**If you want a healthy brain, strong memories and the ability to maximally capture daily information, your best bet is to prioritize sleep. We do know that aging does impair memory formation during sleep. Further studies will likely reveal if indeed memory can be enhanced by mimicking the neural pathways occurring during sleep and stimulating them during wakeful hours.**** See More Helpful Articles:**
Eli Hendel, M.D. is a board-certified Internist and pulmonary specialist with board certification in Sleep Medicine. He is an Assistant Clinical Professor of Medicine at Keck-University of Southern California School of Medicine, Qualified Medical Examiner for the State of California Department of Industrial Relations, and Director of Intensive Care Services at Glendale Memorial Hospital. His areas of expertise in private practice include asthma, COPD, sleep disorders, obstructive sleep apnea, and occupational lung diseases.