There are many mysteries in the world, and there are even more in the way humans think and behave. One of these mysteries is the consciousness, so mysterious that cognitive science has been studying it since time immemorial. However, what cognitive science has just discovered, an ancient Indian philosophy had known it hundreds of years already - that the mind is still conscious even in deep sleep.

Over the years, the Western world held the belief that people are unconscious when they sleep. However, a meta-analysis published just last month showed that there is "experiential or conscious activity" happening during sleep and that it happens during the different stages of sleep.

Evan Thompson, one of the authors of the analysis and a professor of philosophy at the University of Columbia, said that the consciousness that occurs when a person sleeps is more complicated than when a person is awake. This conscious awareness is not something that is preserved in memory but something that has something to do with memory preservation and skill-learning.

Another study shows that there are fast frequency ripples occuring in the hippocampus during deep sleep. This suggests that the brain has to think of the idea that deep sleep is indeed a period of total unconsciousness. What's surprising, however, is that those who practice meditation say that they are conscious when they are sleeping and their brain scans show that there is a high gamma-band frequency as well as distinctive electrophysiological brain patterns compared to those who do not practice meditation.

Thompson said that such belief is seen throughout the ancient texts of the Yoga and the Vedanta. According to these ancient Indian philosophy, the mind is still very conscious even in deep sleep, even when it is not doing any ordinary mental activity.

Thompson said that truly, cognitive science has yet a lot to learn from this ancient Indian philosophy. He added that by melding them - ancient philosophy and cognitive science - together, experts will find treatment for a number of sleep disorders that plague humans nowadays.