We spend about a third of our lives in slumber. Before advances in neuroscience and biology, it was believed that a sleeping person is a passive, dormant being. Now we know that our body, especially our brains work over-time during our sleeping phase, furiously making and breaking neural connections. Sleeping is not just an act of retreat and rest but physical and mental restoration as well. Advancements in science have brought in brain scanning, virtual imaging and other tools to better understand the phenomenon of sleep.
So really what goes in the human body during sleep? What’s the physics behind it? Can we exploit it to our advantage, for example – to enable shared dreaming?
Brain Activity During Sleep
While we sleep, our body has a lot to work on. The rigors of our lives affect every cell in our body. To make up for the damage caused and to prepare itself for yet another day, our immune system needs to get charged up. So it produces antibodies and builds up on its arsenal of cytokines. These, together, fend off any invaders that we face.
During the day our brains has an excessive influx of information and lot of tasks to perform simultaneously. As we sleep, our involuntary actions continue but many of the neurons that were used while we were awake get a mini-vacation and a chance to rid themselves of the byproducts of their cellular activities, thus, cleansing themselves. This is important to prevent neural deterioration.
Another aspect of our lives affected by sleep is our memory. Whatever we do, speak, think and sense is represented in our brains in form of nerve signals. Certain nerve-signaling patterns are repeated during sleep in order to encode these as memories and improve learning.
The part of our brain that governs our functional at a social and emotional level too gets a well-deserved rest as we snooze, which is essential for its proper functioning when we wake up.
One of the greatest impacts of sleeping can be seen in the way it affects children and teenagers. It is during their sleeping period that the growth hormones are released. Building of muscle mass, tissue repair and vital brain growth occurs when asleep. Various developmental processes related to puberty also occur in snooze-time.
Lack of sleep, or sleep-related troubles like insomnia, thus have a detrimental effect. Other than impairing immunity, alertness, memory and growth, sleep deprivation is hazardous directly too. A sleep-deprived driver, for example, is a road hazard while people working irregular shifts or overworked staff is prone to work-related injuries.
The Sleeping Mechanism
Seeing how sleep affects our body to such an extent variably at different stages of our life, it is understandable that the pattern of our sleep cycles vary across our lifespan. While infants require 16 hours of sleep per day, this goes down to around 9 hours for teenagers. As we grow older, we tend to sleep lightly for shorter time spans. But it is not only the length of our sleep but the time when we tend to fall asleep that varies with age. This necessary amount of sleep increases if we remain sleep deprived. We start developing a sleep debt, one that has to be repaid or else borne at the cost of impairment of our judgment, reaction-time and other cognitive abilities.
This can be better understood by delving into the mechanisms of sleep.
Every organism has a certain biological rhythm controlled by an intrinsic ‘clock’. We have such a circadian rhythm (circa = about, dian= 24 hours) that is governed by a pair of brain structures composed of about 20 neurons. This part of the brain, called the Superchiasmatic Nucleus (SCN), works in tandem with the optical nerve system to determine the time of the day. As light goes down and darkness sets in, the SCN sends signals to various parts of the brain, including the pineal gland. This gland secretes melatonin which it had stopped producing in light. As melatonin level rises, we feel drowsy. Since light is a deciding factor here, people with total blindness tend to have sleeping troubles like periodic insomnia. Biological clocks, though, have room for adjustments. These are not set-in-stone rhythms and can be tuned to various cues. Though light is an omnipresent cue, or zeitgeber; ringing alarm clocks, meal times and the garbage truck clatters are some other zeitgebers that affect our body rhythms in present time. Therefore external factors along with chemical and neural systems make us drowsy.
But we do not switch between the states of being ‘Awake’ and ‘Asleep’. When we are falling asleep we go through transient phases which can be described by specific fluctuations of electrical activity that can be measured by electrodes. These fluctuations are seen as brain waves.
Stage 1 of 5
The first stage is light sleep wherein we drift in and out. Our eyes move very slowly, and muscle activity goes down. This is also the stage where we are prone to hypnic myoclonia – sudden muscle contractions preceded by a sensation of falling.
Stage 2 of 5
As we drift into stage 2, our eye movement stops and brain waves slow down. The next 2 stages can be described as deep sleep. It is characterized by extremely slow brain waves (delta waves) interspersed with sleep spindles, or occasional bursts of rapid waves. It is difficult to awaken people who are in this stage.
Stage 3 of 5: REM Sleep
The most interesting stage is the REM (Rapid Eye Movement) stage. This is the time we dream! Our breathing escalates and our eyes start jerking rapidly in various directions. It is believed that by some that dreams are cortex’s (a part of brain that organizes and interprets information during consciousness) attempt to find meaning in random signals. And so, it is possible that the cortex tries to interpret random signals into a fragmented storyline. Our brain areas that retain memory and affect learning are also stimulated. Thus, sleeping aids in making connections and cementing certain memories in our psyche. While these areas are afire with activity, other parts are shut off. One sleep cycle averages to around 100 minutes. Thus, in one night we go through several such cycles. The first REMs are relatively short, with the dream stage increasing in length as night progresses. REM is critical to quality sleep. Caffeinated drinks, certain drugs, alcohol and smoking affect sleep quality and rob us of restorative deep sleep and necessary REM sleep.
During REM, our voluntary muscles are signaled to relax. We experience a temporary paralysis of our limb muscles in REM stage. If this paralysis is somehow interfered with, people may act out their dreams – leading to say, hitting someone while striking a boundary in one’s dream! It is also the source of REM sleep behavior disorders like sleepwalking. But this paralysis should not be confused with the phenomenon of sleep paralysis that occurs in some cases when a person is just falling asleep (predormital or hypnagogic) or just waking up (postdormital or hypnopompic). The people who experience it recount feelings of helplessness as they recognize their inability to move and a constriction on their chest. Such descriptions led to the belief that the said person was possessed by demons. Sleep paralysis, simply put, is the phenomenon of our minds waking up before our physical body. We’re still paralysed as a defence mechanism during sleep – but we’re mentally awake.
But our mind can play games with us too. As healthy as dreaming is, it is probably one of the least understood phenomenon. This is made even more fascinating by its bizarreness. The outlandish occurrences in our dreams are attributed to possible neural connections that our imaginative brain makes. But what about the dreams that are too realistic?
A manifestation of this situation is a false awakening, a dream that is vivid in detail and descriptive of a normal schedule of the dreamer, which convinces the person that they are awake or even, in rare cases, convinces them that they have woken from a dream. These phenomena of false awakenings and dream inside a dream phenomenon have been a source of intrigue and screenplays. Inception dealt with multiple dreams contained in other dreams, Waking Life also represented false awakenings.
But the peculiarity doesn’t end here. While there are fragmented reported cases of conditions like the exploding head syndromes (imaginary noises when falling asleep or waking up) and precognitions (apparent dreams about events yet to occur), some studies about dreams lead to the disturbing world of schizophrenia. Some analysts believe that the scans showing active regions of the brain when dreaming in REM are comparable to scans of schizophrenics. While we ascribe our weird dreams to nerve circuits reaching out for some connections resulting in an amalgam of unrelated memories, in cases of schizophrenia and probably other mental impairments, these circuits flare up randomly when the person is awake. Simply put, the dream knob doesn’t turn off for them even when they wake up. Conversely, we can say that our nightly dream excursions are our own slice of madness.
So, are you awake? Or are you dreaming? Scores of articles on the web try to give tips on how to ascertain our reality, to check whether you are awake or dreaming, lucidly. Suffice to say that a thing like jumping off the roof to see if you are dreaming is a very dangerous act indeed (Again – Inception, anyone?). Besides, it can be argued that our supposed reality is also a figment of imagination or a dream of an unknown entity but that is a debate for the philosophers.
As of now, I can assure you that you are awake. Because I highly doubt that you dreamt up this article! Or maybe you did.