MRI helps unravel the mysteries of sleep

Brain activity during sleep

After checking, analyzing and comparing all the data, what Tarun found was surprising. "We calculated exactly how many times networks made up of different parts of the brain became active during each stage of sleep," she says. "We discovered that during light stages of sleep - that is, between when you fall asleep and when you enter a state of deep sleep - overall brain activity decreases. But communication among different parts of the brain becomes much more dynamic. We think that's due to the instability of brain states during this phase." Van De Ville adds: "What really surprised us in all this was the resulting paradox. During the transition phase from light to deep sleep, local brain activity increased and mutual interaction decreased. This indicates the inability of brain networks to synchronize."

The role of default-mode networks and the cerebellum

Consciousness is generally associated with neural networks that may be linked to our introspection processes, episodic memory and spontaneous thought. "We saw that the network between the anterior and posterior regions broke down, and this became increasingly pronounced with increasing sleep depth," says Van De Ville. "A similar breakdown in neural networks was also observed in the cerebellum, which is typically associated with motor control." For now, the scientists don't know exactly why this happens. But their findings are a first step towards a better understanding of our state of consciousness while we sleep. "Our findings show that consciousness is the result of interactions between different brain regions, and not in localized brain activity," says Tarun. "By studying how our state of consciousness is altered during different stages of sleep, and what that means in terms of brain network activity, we can better understand and account for the wide range of brain functions that characterize us as human beings.