The large body of studies pursued in the past decade shows how much interest is sustained in the indispensability of sleep in the different functions of the human body including its role in learning and memory.
Initially, past researchers focused only on Rapid Eye Movement (REM) stage and supposed that sleep is merely passively involved in the retention of memory.
But recent findings[5] exhibit otherwise: the discovery of Slow Wave Stage (SWS) and its active role in the consolidation of memory shows the significance of sleep in the overall processes that occur in the brain, which ultimately affects its function in relation to the entire body systems. Other key findings also unravel the fundamental neurochemical, electrophysiological and genetic mechanisms that develop during the sleep process.
The Slow Wave Sleep is the second stage in the non-REM sleep cycle, right after light sleep stage. Studies suggest that the consolidation of episodic or fact-based information (those that answer the question ‘what’) happens in this stage, while the consolidation of both emotional memory and procedural or how-to-do skills occur during the REM cycle.
These studies agree with the same conclusion of what was discussed in the preceding section, that the waking cycle is indeed an encoding stage for memories. The sleep cycle, on the other hand, is the consolidating stage.
As further observed, the Slow Wave Sleep is where the process starts during the memory consolidation stage. Newly registered pieces of information in the form of neuronal representations are reactivated during the SWS and are then transferred for integration into long-term memory. In other words, the transformation of short-term memory into long-term occurs during the SWS. The consequent REM cycle then serves to stabilize this recently stored information in the brain.
In a sense, the retrieval of information does not only happen by conscious effort. Automatically, it also occurs during the Slow Wave Sleep stage of sleep, where the short-term memory is reactivated and transferred into long-term storage.
Another study[6] published in Psychological Research notably concludes that during the consolidation process, the brain is selective with what type of memories it wants to reactivate. This reinforces the theory that not all memories are reactivated and consolidated.
They undergo filtering during sleep as well. This may give us an insight as to why temporarily stored memories such as crammed lessons are easily forgotten – because they haven’t been really consolidated and processed in the first place.
Accordingly, the preference in memory consolidation is based on “future plans” or what had been consciously thought of as relevant during the waking stage of information acquisition. The significance of this finding will be elaborated more in later chapters in this book relating to focus and concentration, as these are the types of skills that are manageable by the subject learner during the conscious phase.
It is also important to note that the duration of Stage II of non-REM sleep or SWS is determinant of the integrity of memory consolidation. This explains why people with serious insomnia may have trouble remembering facts-based or non-emotional information.
Reduced amount of SWS is likewise common as people get older, which is the reason behind what is said to be a sleep-related memory decline in most ages starting at 30 and over.[7]
So you see, forgetting often is not really a natural result of getting older itself. While adulthood is a factor associated with lack of sleep, it may not necessarily be the case if we only try to improve our sleeping habits for better memory and well-being.