Sleep remains a mystery despite all the research done so far. Science says it helps to consolidate our memories and remove unnecessary information. It says, during sleep, when inputs from our five senses are almost zero, the ‘mind-brain’ takes stock and helps to consolidate memory learned during the day. However I think we sleep because it is like forced meditation; it invigorates and charges our batteries.
In sleep, we go through four or five cycles of deep sleep and dreaming episodes, each of 90 minutes duration. Electroencephalography (EEG) studies done on the human brain (during sleep) show that deep sleep is characterised by production of low frequency delta waves known to help produce life and mood-enhancing chemicals. Here, we are totally unaware of our surroundings. But, dreaming episodes characterised by the rapid eye movement (REM) stage is of light sleep; you can be woken up quite easily. Hence when we wake up after a deep sleep it is refreshing and invigorating.
In deep Samadhi also one produces delta waves, though most studies of the meditating brain show prevalence of Alpha waves, perhaps because EEG and FMRI are quite invasive and so are not conducive for deep meditation. The noise and intense magnetic field of FMRI and electrical wires of EEG dangling around the subject’s head do not create a conducive environment for deep meditation. Nevertheless, studies of EEG on some have shown that in deep meditation there is a spike in delta wave production.
Outward signs of losing complete consciousness are similar to that in deep sleep. Ramakrishna Paramhansa, when he attained enlightenment, was completely oblivious to the world for almost six months. To keep him alive during this time his guru force-fed him.
In deep sleep, most of the peripheral brain neuron activity either reduces drastically or shuts down. Only the central portion of the brain – seat of autonomous nervous system — works. This is also where long-term memories are stored and consolidated.
Much irrelevant information takes up memory space. As the peripheral brain shuts down these memories get dissolved, allowing the brain to increase its processing power for yet another day.
Deep meditation also allows removal of sanskars or memories as sage Patanjali stated and this could be a probable mechanism to do so. In fact he defines yoga as suppression of thought waves; so the low frequency delta waves in deep sleep could be a manifestation of this process.
When deep sleep is disrupted, memory dissolution doesn’t take place; memory knots keep growing, creating irritable moods and short tempers. There is also a growing body of data in sleep research indicating that in many people who are not getting enough restful sleep, the incidence of diabetes, heart problems and even cancer are increasing.
Brain under anesthesia also produces low frequency waves, but only in the fragmented brain. The communication between different parts of brain is stopped by anesthesia chemicals. However in deep sleep the whole brain is as active as in deep meditation.
How do we induce deep sleep? One way is by doing daily vigorous exercise and meditation. Both help in dissolving temporary memory knots and producing conditions for better sleep.
Deep sleep is also helped by reducing external inputs like sound and light. Thus people who sleep in lighted environment do not get deep sleep, though extensive REM activity takes place. Similarly when there are too many worries and the mind is not at peace, one cannot sleep deeply.