Researchers have determined that during the deepest part of sleep, the mind acts like individually working sections. When we are awake, the brain behaves more like a network, with different sections connected by synapses.
The researchers used a magnetic field to generate an impulse in the brain and then studied how that perturbation traveled throughout the brain. They found that while awake, the signal would travel around the brain relatively easily. However during deep sleep, they found the signal died very quickly. The researches believes this means the brain is more compartmentalized during sleep.
Here is the link: http://www.livescience.com/humanbiology/050929_bra in_sleep.html