Relationship between memory and sleep: is it truly a myth?

There are different types of memories they could be fact based (such as remembering a country’s capital), episodic (connected to specific events like your first kiss), while some are instructional (involves learning). All of the types of memories goes through the same process to become memories these processes are: Acquisition (first exposure to a new experience or knowledge), consolidation (stability of the memory in the brain) and recall (accessing the memory in the future). Acquisition and recall occurs during the state of wakefulness while studies have shown that consolidation occurs during sleep.

According to a study published in neuroscience news in 2014,”Brain cells that spark as we digest new information during waking hours replay during deep sleep, also known as slow-wave sleep, when brain waves slow down and rapid-eye movement, as well as dreaming, stops. Scientists have long believed that this nocturnal replay helps us form and recall new memories, yet the structural changes underpinning this process have remained poorly understood”. However, during this study the scientists were able to track and image the growth of dendritic spines along individual branches of dendrites before and after mice learned to balance on a spin rod.  The mice sprout new spines along dendritic branches, within six hours after training on the spinning rod, the researchers set out to understand how sleep would impact this physical growth. They trained two sets of mice: one trained on the spinning rod for an hour and then slept for 7 hours; the second trained for the same period of time on the rod but stayed awake for 7 hours. The scientists found that the sleep-deprived mice experienced significantly less dendritic spine growth than the well-rested mice. Furthermore, they found that the type of task learned determined which dendritic branches spines would grow.

This study thus explain why new knowledge are better retained after period of sleep/rest.

Interestingly, sleep has been implicated in the process of dementia and Alzheimer’s  disease development. According to a publication by Alzheimer’s disease association, it was found that beta amyloid (the protein that builds up in excess in victims of  Alzheimer’s disease), was found to be elevated in patients that reported poor sleep/sleep deprivation. Another study was conducted to determine if the beta-amyloid build up is the cause of poor sleep or if poor sleep precedes beta amyloid build up. The result of the study shows that 22 years after initial sleep length and quality assessment, investigators assessed the subjects’ cognitive function and found that lower cognitive scores were found in individuals who reported the following:
• Short (<7 hours) or long (>8 hours) hours of sleep at midlife compared to 7-8 hours per day.
• Poor sleep quality.
• Use of hypnotics for 60 or more days per year. Hence the conclusion was that sleep actually do play a role in development of dementia/ Alzheimer’s disease.

The good news is sleep quality can be improved by exercise and sleep duration can be controlled. So, the next time you are planning on reading through the night for a test or presentation; remember your memory can only be consolidated by sleep and that is important to prevent the build up of beta amyloid in your sharp brain.

REFERENCES

Sleep Deprivation and Memory Loss  http://www.webmd.com/sleep-disorders/sleep-deprivation-effects-on-memory#1

Abstract for “Sleep promotes branch-specific formation of dendritic spines after learning” by Guang Yang, Cora Sau Wan Lai, Joseph Cichon, Lei Ma, Wei Li, and Wen-Biao Gan in Science. Published online June 5 2014 doi:10.1126/science.1249098

Alzheimer’s disease: What’s sleep got to do with it?  https://www.alz.org/documents_custom/InBrief_Issue5.pdf