Memory and Sleep

Introduction

The connection between sleep and memory has interested lots of scientists from different spheres. Though lots of experiments have been carried out about this connection which gave us huge information about these two phenomena many questions remain unanswered for the majority of people. Excluding some phenomenal people who managed to lead a normal life without getting sleep or little sleep for all of us, sleeping plays a vital role the lack of which may cause enormous problems in emotional, physical, and mental fields.

Types of sleep regimes…

There are two types of sleep regimes polyphasic and monophasic. The first type is the practice of sleeping multiple times (usually two or more) during 24 hours following some sleep regimes. There are four kinds of polyphasic sleep. These are 1) Biphasic sleep – Sleep is divided into two scheduled segments. The longer part is at night and takes 5-7 hours and a nap of 20 minutes during the afternoon. 2) “Everyman” regime (regular regime) - The Everyman method consists of a nighttime core sleep period of about three hours plus three scheduled 20-minute naps. 3) Dymaxion regime – this consists of 4 scheduled 30-minute naps every 5.5 hours. 4) Uberman regime – this consists of 6 scheduled 20-minute naps every 3 hours and 40 minutes. Monophasic sleep is what most people would call a regular sleep pattern. A person sleeps 7-9 hours (even 6-10 hours) per night. This sleep pattern is the most widespread and is adopted by the majority of people that’s why we will discuss this one, which is examined more thoroughly than the other types. The polyphasic type is also essential, but we are not going to explain it now.

Monophasic sleep and its phases…

Scientists prove that there are two stages of sleep; non-rapid eye movement and fast-wave sleeping (active, paradoxical). The second one is discovered by Eugene Aserinsky and Nathaniel Kleitman who called this stage rapid eye movement (REP). The combination of these two stages is a particular cycle which is repeated 4-6 times during normal sleep. During the first cycle NREM lasts longer (almost 80-90 minutes) than REM (generally 5-15 minutes), but then it becomes shorter, and REM becomes longer from cycle to cycle.

Some important experiments…

The consolidation of memory…

For a long time, scientists believed that some processes occur in our memory during the process of sleeping. We analyze the information that we get during some days and either fix it in our memory or forget it. We all know that not all parts of information can be transferred from short-term memory into long-term memory. Some parts of the information are not noticed because they are not important. But in most cases even the important parts are not transmitted because of sleep disorders, as according to some scientists the process of consolidation occurs very actively during sleeping.

How does this happen?

Wen-Biao Gan and his colleagues from New-York university decided to understand what happens to the neurons of our brain during the process of consolidation. They synthesized a special fluorescent protein into the cytoplasm of cortical neurons of genetically modified rat. Through which they could examine what was happening with the neurons of the rat, for example where the dendritic spines appeared, which appearance hints that the neuron can communicate with another neuron and the communication can be achieved when, for example, the axon of the other neuron joined to the dendrite of that neuron via synapse. Synapses create neural networks which are necessary to form memory. For example, when we learn to ride a bicycle, a special neural network is created. Then when we repeat our actions, the connection between the neurons becomes stronger through the consolidation of synapses, and gradually we don’t need a special concentration for riding a bicycle, because when we start riding the already developed neural network becomes active through which we do our movements mechanically. Let’s return to the rat. Scientists put it on running wheel and examined what was going on with it while it was trying to keep balance. Dendritic spines started to appear in the movable part of the rat’s cerebral cortex because it was doing something important to its life. Then the scientists somehow changed the conditions of the experiment and adding more mice put them on the running wheel for an hour and let some of them sleep for 7-8 hours while others were still on the wheel. They discovered that during the process of sleeping dendritic spines grew more rapidly and by this way, they influenced the process of memorizing the information, and this happened during the NREM. So we can conclude that we get information when we are awake which activates our neurons then during the process of sleeping those neurons again get activated to fix the information through repetition, even new connections between neurons are created when needed. So the scientists’ hypothesis about the importance of sleep in the consolidation of memory is proved.

The lack of sleep and Explicit (declarative) memory…

To experiment, scientists chose a few healthy people and divided them into two groups. All of them were given the same task, to learn some words. Some of them had a positive meaning, some of them negative and others were neutral. Then the people of the second group were sent to sleep while the first group stayed awake for 36 hours. After all this, they were given a test to understand how sleep had influenced on the learning process of the material and they discovered that participants of the second group remembered 40 percent fewer words than the ones who had slept. But the final part of the experiment was more interesting. Scientists wanted to know what kind of words (positive, negative or neutral) people of the first group (who had not slept) remembered better. The results were surprising. Those who had slept remembered 60 percent more positive and neutral words, but both groups remembered almost the same quantity of negative words. So the lack of sleep causes to forget the information, as well as to memorize negative information better than positive information. In the result of this, we may even start to like negative information and get addicted to it.

After 11 sleepless nights…

17-year-old American Randy Gardner who wanted to set a Guinness World Record stayed awake for 11 days. Neurologist John Rose asked him to subtract seven from 100, then again subtract seven from the number he got and do this continually. When reaching 65 (subtracting 7 5 times), Randy stopped it without any reason. After a minute Rose asked why he had stopped the calculating process to which Randy gave a rather shocking answer “But what should I calculate?” Yes, you are right! That guy forgot the task. So, serious sleep disorders lead to the disorder of memory, which occur with those people, who have senile dementia. By the way, Randy succeeded to set a global record staying awake for 264 hours. After setting the record, he went to give a conference talk and immediately after the conference he went to sleep. He slept 15 hours and woke up cheerful and healthy. He started to sleep a bit longer than average but that continued only for a few days, and soon he adopted a regular sleeping schedule, and after some days his organism was restored.

Conclusion

There are lots of experiments about this topic, but these three ones are already enough to understand how important the sleeping process is for memory and why it is important. Here are four conclusions; 1) The processes of memory consolidation occur during the sleep which improves the connection between long-term memory and short-term memory. 2) The lack of sleep causes consolidation process disorders because of which information can be forgotten. 3) The information is fixed and stored in memory better when we sleep after reading it (even not so long). 4) The lack of sleep after learning information can cause to the bad memorization of that information.