Psychology

This paper involves different literature regarding sleep on the consolidation of memories. It discusses different articles citing the significance of sleep in the improvement of the different aspects of memory. It also includes an integration of all literature and studies mentioned.

Importance of Sleep on the Consolidation of Memories
Introduction
What is sleep According to a medical website,  Sleep is triggered by a complex group of hormones that are active in the main, and that respond to cues from the body itself and the environment  ( Definition , n.d.). Roughly 10 hours of sleep is recommended for children while 8 hours are needed by an average adult person. According to Michel Billiard and Angela Kent, sleep has fascinated man for centuries. It is part of the human life cycle. They referred to it as  an escape from the daily hardships of life, a mysterious state, where gods may communicate with man  (2003). It is a mystery for the very question of why we sleep still remains unanswered (3).

It is important for every human to sleep. In fact, sleep has many advantages. Benefits of sleep cover almost every aspect of human life. Sleep helps repair the body. During sleep, the body produces extra protein molecules, repairing damaged tissues and relieving stress. Sleep also takes care of the heart by reducing its levels of stress and inflammation. It also helps in the consolidation of memories ( The Benefits , 2008).

Sleep and Memory
In an article entitled Sleep, Memory, and Plasticity, the importance of sleep on the consolidation of memory is discussed (Walker et al., 2006). The article is basically a review of different findings regarding the role of sleep in memory encoding, memory consolidation, brain plasticity, and memory reconsolidation. According to them, the hypothesis of sleep having to do with memory development was unheard of until the time of the discovery of rapid-eye movement (REM) and non-rapid-eye movement (NREM) sleep in 1953.

In the past, studies have shown that after information has been recalled, memory returns to an unstable state, thus requiring consolidation or reconsolidation (Walker et al., 2006). Basically, these studies have conceptualised the consolidation of memory into at least four processes. These processes are reactivation, leading to destabilisation, which leads to either degradation of reconsolidation. In the article of Walker et al., they have hypothesised that the processes of degradation and reconsolidation must happen in the period of sleep.

In 2002, a study was conducted regarding the effect of sleep on memory for finger skills. The study was conducted by Stefan Fischer, Manfred Hallschmid, Anna Lisa Elsner, and Jan Born. They explained that when practicing a motor skill, a process of memory consolidation is triggered, which continues on even the practice has ended. More interestingly, the skills improved after a later testing.
Fifty-two participants were involved in the experiment. These participants were healthy with no experience of any form of sleep disturbance. Also, none of them had an experience in playing a musical instrument or in typing. The experimenters made use of a finger-to-thumb position task that followed a sequence. The participants were tasked to perform this without looking at their hands. Their performances were recorded before and after sleep. Results from the correlation coefficients showed that there was an increase in the performance of the participants who had high amounts of REM sleep.

According to David N. Neubauer,  Forgetfulness is a common complaint of people who do not get enough sleep, whether it is due to sleep deprivation from an overly busy schedule or the result of insomnia.  (2009). In his article entitled,  Sleep and Memory , he explained that there are plenty of evidence supporting the conclusion that post-learning sleep consolidates both declarative and procedural memory (20). He further stated that sleep can stabilise memory, making it more resistant to interference from other learning tasks, generally improving memory tasks. He continued, saying,  Night time sleep significantly improves memory test performance, but even daytime naps following learning tasks offer subjects benefits compared to individuals tested after the same intervening period without sleep  (20).

Another experiment was conducted by Steffen Gais, Werner Plihal, Ullrich Wagner and Jan Born regarding the effect of sleep on memory (2000). The experiment involves practicing visual texture discrimination. To establish the effect of sleep in the task at hand, they compared performances between after an early sleep and after a late sleep, which is dominated by slow wave and rapid-eye movement sleep. It showed that the improvement of the task is dependent on sleep. Results showed that improvement on visual texture discrimination was evident after early sleep, even more after a whole night sleep, but did not show any improvement after late sleep alone. The results of the experiment suggested that procedural memory formation is prompted by sleep-related processes. It also suggested that late REM sleep may improve memory formation but only at a second stage, after two periods of early sleep.

The same conclusions were concluded by a study made by Steffen Gais1, Brian Lucas, and Jan Born. They performed two experiments, which suggest that sleep has a persisting effect on hippocampus-dependent declarative memory (2006).

In the first experiment, they investigated whether sleep within a few hours of learning in the evening enhances the consolidation of memory. Twelve American high school students participated in the four-condition experiment. For each condition, the participants learned one of 24-pair English-German vocabulary lists with a limit of 10 minutes. The results showed a significant difference among the number of forgotten words between the morning-learning condition and the evening-learning condition. The participants in the morning-learning condition got the most number of forgotten words than in the evening-learning condition.

The second experiment determined if this evening-learning condition could be attributed to sleep following learning or whether it was dependent on the time of day. Fourteen male high school students participated in the experiment and were divided into two conditions. In the first condition, the participants were given the same task as in the first experiment. Afterwards, they went home to sleep. The other condition was the same, only that the participants did not sleep.

Results of the second experiment showed that there was a significant relationship among the number of forgotten words between the two conditions. The results pointed out that there was a very high percentage on the number of words forgotten in the sleep-deprived condition, as compared to the condition where participants slept.

Summary
In conclusion, sleep has a great effect on the consolidation of memory. This proven fact was established by Walker et al. when they discussed the different findings on the importance of sleep on memory and plasticity. The experiment conducted by Fischer et al. has supplemented the claims of Walker, proving that sleep has an effect on memory even in improving motor-related skills. On the other hand, David N. Neubauer was able to determine that forgetfulness is a being caused by lack of sleep or disorders related to it. He also added that even nap time during any period of the day can already increase memory-related performance. Even in improvements on memory through vision, sleep proved to be very effective as concluded by Steffen Gais, Werner Plihal, Ullrich Wagner and Jan Born in their experiment. The same conclusions prevailed after an experiment by Steffen Gais1, Brian Lucas, and Jan Born, where they were able to generalise that sleep has a significant effect on hippocampus-dependent declarative memory.