Targeted Memory Reactivation at The Forefront: Sleep as a Critical Memory Consolidator

Memory is something that has been throughly examined for centuries. Aristotle once described it as being "the sum of experiences" a person goes through in life. To some extent, Aristotle was assertive, but why is it that some memories are stronger than others? How can the study of memory enhance such experiences and even create new ones?

Memory has always been a center of interest in humanity, however, it hasn't been until recently that researchers have made significant contributions to the this area. Whereas memory was once considered simply a recollection of experiences, it is now looked at as a necessary skill to continue learning. In efforts to optimize learning and knowledge acquisition, memory is now studied. More importantly, scientists are shifting their focus towards the factors that affect memory, and how it is that the positive factors can be intensified to prolong memory as we age.

Knowing that memory deteriorates with age comes to no surprise to all. Often the question was: why is memory corrupted with age? Now the question is: how can we enhance brain health and promote good memory? Which leads to the focus on the brain to gain a more comprehensive look towards it.

As we continue to better comprehend the brain, different methodologies to improve memory are being formulated. Cognitive diseases have raised many questions for researchers; something that has been beneficial to revolutionizing scientific investigation of memory. Today, in order to increase memory , people tend to practice mind or brain exercises, take part in repetition and different learning activities, or even adjust their diets to increase memory retention. Unfortunately, sleep has been a memory enhancer that has been ignored despite the factual evidence showing its benefits.

Scientists have many times expressed the importance that sleep has in the learning process. College students are strongly discouraged from pulling all nighters, and progressive studying is advertised as more effective rather than learning material in bulk. Notwithstanding the scientific findings proving sleep to be extremely necessary for overall well being, people still tend to deprive themselves of it and function on just a few hours of sleep. According to StudyFinds, Americans show to average less than 6 hours of sleep, while the recommended sleep time falls between the 8-9 hour range. In adults, this can be extremely detrimental to health. Insufficient sleep a driver of easier memory loss, unproductiveness, lack of creativity, and overall cognitive function decline. Lack of sleep is dangerous; it is the equivalent to being under the influence.

So if sleep is so necessary for health, cognition, and learning in adults, imagine its heightened importance in children growing up- their neuronal development is in constant updating. During sleep, children can increase their learning, memory retention and consolidation. Sleep can collectively prepare children to become better learners, problem solvers, and artists.

Understanding Memory

It is now recognized that episodic memories including the: who, what, when, where, why memories, are stored into the cortex via the hippocampus; an area from which they can be retrieved. The hippocampus, therefore, has been of central focus to study the memory processes and formulations.

In the search for new memory enhancers, Target Memory Reactivation was created. Target memory reactivation (TMR) is a recent modern method which has shown to improve the retention of memory during sleep. However, TMR's benefits are still being tested in terms of applying these memories into real world conditions- such as learning vocabulary. Some studies show that TMR is dependent on habituation and sleep disturbances. While others pin point it as a standing ovation. Overall, it is important to consider the factors that can prove determinant to memory retention and then adapt what is useful.

TMR Explained

Exposing a person to memory cues during NREM Sleep has shown to later enhance memory performance; this is what TMR aims at doing. This is a technique that takes sensory or verbal cues before sleep and then plays them during sleep through uncued items. The early hypothesis while experimenting with TMR was that there would be a reactivation of neuronal memory movements in the hippocampus when stimuli was presented. Such positive effect of TMR has now been supported. Now different experiments pertaining to TMR are being carried out, looking at memory during sleep while providing different cues including odors, sounds, melodies, or even verbal material.

Established Research

In an experiment consisting of 66 healthy individuals, the participants were instructed to learn the same 120 Dutch German word pairs over a period of 4 days. Afterwards, the participants slept in their normal environment and half of the words were played/ cued during sleep over the three nights. The hypothesis was that these words would be retained better. However, sleep disturbances had a significant impact on memory. The results of this study showed that as the days went by and TMR was used, the participants recalled more words. Those that experienced the sleep disturbance factor didn't show any benefits. TMR also showed to have word gains for cued words, the only problem was that the same cues could create sleep disturbances in some. At the end of the experiment, the conclusion was that unsupervised TMR does not show a significant beneficial memory effect on an uncontrolled environment based off using cueing vocabulary from a foreign language. Another finding was also that the TMR effect is effective only from participants that have pre existing knowledge and to-be learned objects .

To contrast the experiment mentioned, let's shift to the odor factor instead of the sound factor. This study involved presenting odors during sleep, and TMR was examined based on brain hemispheres. The hypothesis in this experiment was that if the odor was presented only to one nostril, memories would be affected and therefore would only modulate sleep oscillations associated with a specific hemisphere. The researchers confirmed this hypothesis and concluded that TMR selectively enhances hemisphere related memories for specific words. The odors were presented during NREM sleep through one nostril (unilateral). Learning was then observed; based on contextual odor.

Sleep has shown to be supportive of different types of memory performance including declarative spatial, procedural, emotional, and perceptual. It has also been showed that memory pertaining to the hippocampus occurs in two steps; from encoding information when awake and then to a transfer of information in the neocortex during NREM Sleep. TMR investigation shows many promises, with odor as a good stimuli- because it doesn't disturb sleep. Odor is also a powerful cue because of its direct projections from the olfactory cortex to the hippocampus. The question with TMR is if it affects memory only at a local or global perspective. This would be reflective of the effects in cortical sleep oscillations.

Let's look at another study, where the retrieval of knowledge related to neuronal activity was investigated. The learning in the study was driven by motor learning. An object was presented and accompanied by a related sound, then the sound cues were presented during sleep. With the idea that memories are retrieved during sleep, the researchers concluded that memories would also be stabilized; something that was supported by examining electrophysiolofical signals triggered by movements and cued memories. The presence of sleep spindles in brief oscillation activity had also shown to engage memory, therefore scientists paid close attention to oscillations.

Although some studies have strongly supported TMR as an effective method to drive memory consolidation, others have recorded a weaker relationship. In education, however, it is salient to consider such effects of sleep on learning and memory.

Sleep and Education

Sleep can amplify training and skill acquisition. Even something as short as a 6 minute nap has shown to contribute towards memory processing.

If the exertion of positive effects on memory function are so apparent, then why are educational institutions not listening to science? What are educational institutions doing to improve learning aside from practicing brain health promoting activities? What are educators doing to promote sleep, to enhance children's ability to build on their memory strength? How have scientific findings affected the way in which schools are conducted? All of these are questions that both parents and educators should be acting on. It's not only about asking the right question, but about being responsible of the answer.

Elementary and Middle Schools have a school start time as early as 7:30am, requiring some students to wake up at extremely early hours. This is relevant because children in these grade levels are developing neurologically- thus disrupting sleep or even depriving of the sufficient sleep suggested (9-12 hours) would be detrimental and cathartic to memory and learning. Should school times be adjusted to a later time? Studies by CDC show that 6 in every 10 middle schooler doesn't get enough sleep. This means that 60% of students in middle school lack the necessary fuel to ignite their creativity and learning.

Sleep as a Takeaway

There are different memory consolidation processes that are necessary to retain information, and sleep is a critical player which should not be ignored. With different leaning and memory methods can come different implementations which may seem exciting. Playing instrumental music while studying, appealing to learning styles, or even promoting TMR could all be effective. The key takeaway, however, is that all these stimulants will not reach their potential with insufficient sleep. Educators may implement different ways of teaching, but institutions should look at the overlooked factors that contribute to learning. Schools control at what time students come in to learn. The power is in looking at what is not usually looked at; this approach could promote success and persistence.

Starting with the intrinsics of neuroscience can lead to the externalities of humanity. It is with such convergence that we can become learners fueled by curiosity and not knowledge engrained by imposition.

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My wish is that you learned more about TMR and that sleep becomes part of one of the priorities of the world.

Hemingway once put it in a rather interesting way when he said "I love sleep. My life has the tendency to fall apart when I'm awake, you know?”

Funny enough, he is talking about the chaos life brings and comfort of dreams and rest- showing that he prefers indulging in sleep.

However, if sleep brings dreams and sparks curiosity- couldn't this time away from the conscious bring great things when awake?

Sleep and dream.

Rest.

Sleep to rest and from that will come a restlessness to learn.

What comes next is exciting, Wonderers!

Sources

Bar, E., Marmelshtein, A., Arzi, A., Perl, O., Livne, E., Hizmi, E., Paz, R., Sobel, N., Dudai, Y., & Nir, Y. (2020, March 5). Local Targeted Memory Reactivation in Human Sleep. Current Biology. https://www.sciencedirect.com/science/article/pii/S0960982220301718.

Göldi, M., & Rasch, B. (2019, May 2). Effects of targeted memory reactivation during sleep at home depend on sleep disturbances and habituation. Nature News. https://www.nature.com/articles/s41539-019-0044-2.

KP;, J. B. P. S. S. M. V. A. C. W. (n.d.). Use of targeted memory reactivation enhances skill performance during a nap and enhances declarative memory during wake in healthy young adults. Journal of sleep research. https://pubmed.ncbi.nlm.nih.gov/30740838/.

Wang, B., Antony, J. W., Lurie, S., Brooks, P. P., Paller, K. A., & Norman, K. A. (2019, August 21). Targeted Memory Reactivation during Sleep Elicits Neural Signals Related to Learning Content. Journal of Neuroscience. https://www.jneurosci.org/content/39/34/6728.