Tick-tock-tick-tock, it’s 5 minutes to midnight. Tomorrow is your big chemistry exam followed by a guitar audition in the evening. You have been studying and practicing for weeks but you still don’t feel ready. What would you do?

  1. Spend the next few hours practicing and cramming everything
  2. Go to sleep

Sleep isn’t lost time?

Fig.1: Working Overnight

For most of us, the answer would be one. Going on the phrase where desperate situations require desperate measures, many of us give little attention to sleep. This goes with the common misconception that sleep is just a way to rest when all the important work is done. But sleep is an important procedure that affects respiration, regulating circulation, growth, and immune responses. One-fifth of the circulatory blood of the body is channeled to the brain while we sleep which is vital in restructuring memory. A minimum of 7 hours of daily sleep seems to be necessary for proper cognitive and behavioral functioning.

The Forgetting Curve

According to the research done by Hermann Ebbinghaus(1850-1909), people tend to forget rather quickly after learning material, and the progress of forgetting slows down with time. His studies revealed that we usually forget 40% of new material in the first 20 minutes. This is under the phenomena known as the Forgetting Curve. It shows the loss of information over time when there is no attempt to retain it. Despite the forgetting curve is a natural process, this can be disrupted.

Fig.2: The Forgetting Curve

In real life, the forgetting curve starts at around 75% because the new material will not retain entirely after a lecture. However, a dramatic increase in memory is shown with immediate reviewing as soon as a lecture finishes. Yet again without additional intervention, the new content loses in time.

The Hippocampus

Fig.3: Location of the Hippocampus

This process can be controlled by memory consolidation. It happens when information is transferred from our short term memory to long term memory. This is mediated by a major part of the brain known as the Hippocampus. It is a seahorse-shaped structure in the cerebral cortex’s medial temporal lobe.

The famous studies were done with patient H.M. where his Hippocampus was removed and was unable to form new short-term memories. His ability to form long term memories were also damaged. But he was able to learn physical tasks due to repetition. This proved that the Hippocampus is responsible for Declarative memory consolidation rather than Procedural memory. Declarative memory includes facts and concepts that are tested in the chemistry exam. Procedural memory includes the hand movements, finger movements that have to be mastered for the guitar solo.

Sensory data are transcribed and temporarily recorded in neurons as short term memories. Hippocampus functions informing and strengthening new connections between neurons, where information will be returned as long term memory to the cortex.

Memory Consolidation

Memories formed under stress are better recorded because there is a direct link of the hippocampus with emotion. That’s the reason where most new information will go to memory fast when it’s close to the exam. But staying awake overnight cramming them will lead to memory loss which affects badly for the exam. Hence one of the most important factors that contribute to memory consolidation is a good night’s sleep.

Fig.4: Brain activity during REM sleep(right image) and being awake(left image). (Red color shows greater activation).

There are different classifications on stages/phases of sleep.  This includes nodding off, light sleep and deep sleep followed by the two important phases,

  1. Non-rapid eye movement(NREM)
  2. Rapid eye movement(REM).

EEG Studies

Fig.5: EEG studies of a mice brain during the wake, NREM, and REM sleep.

EEG studies of the brain in people undergoing rapid sleep have revealed the flow of electrical impulses between the Brain stem, Hippocampus, Thalamus, and the Cortex.

In REM sleep the eyes move rapidly and randomly below the eyelids where the brain becomes active. Breathing becomes faster compared to NREM sleep and the blood pressure and heart rate rise almost to walking levels.

Different sleep phases consolidate different memories. During NREM, declarative memory is encoded into a temporally store in the anterior part of the Hippocampus where the electrical impulses drive it to the long term memory storage in the cortex. REM phase is associated with the consolidation of procedural memory.

Plumbing at Night

Recent studies state that the brain eliminates toxins in a plumbing system known as the glymphatic system associated with the glial cells in the human body. Glial cells regulate the flow of cerebrospinal fluid (CSF). CSF is important for waste removal in the brain which happens during sleep. Very recent insight on waves of watery CSF flow over our brains, pulsing rhythmically, removing unwanted material while we sleep. In NREM, CSF waves wash out unnecessary proteins and other redundant debris.

Fig.6: Rhythmic waves of CSF.

Sleep Tight!

A good night’s sleep will not only affect the long term health, but it’s more likely that the individual will retain all those facts and practice from the previous night.

Sleep can be enhanced by making sure your room is dark. Make sure you are not looking at bright screens including computers, mobile phones an hour or two before going to bed. A cooler temperature will enhance sleep since the low temperature is necessary to signal the brain that it’s time to sleep. Stressed, restless situations will make it troublesome for you to sleep. In such situations avoid staying awake on bed. This trains the brain that bed is not a suitable place for sleeping. Reading a book under a dim light will be a remedy until sleepiness returns. The use of Caffeine will keep you awake with stimulating wake-ups during the night.

Fig.7: Caffeine to the rescue?

Tick-tock-tick-tock, it’s 2 o’clock in the morning. You still have time for the exam. Will you stay all night? Or simply sleep on it? The choice is yours!

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