Sleep and consciousness
During sleep, our brain slips into autopilot. The key change, it seems, is the loss of communication between different areas of the brain
Each day, when we fall asleep, we depart consciousness. The sleeping brain has long puzzled scientists, who have noticed that even though consciousness fades the brain remains active.
Vivid dreams are similar to a ‘virtual reality’ experience. Intensely visual dreams light up the visual cortex, nightmares trigger activity in the amygdala, and the hippocampus flares up from time to time to replay recent events. The pathways that carry signals from the auditory cortex are also active, as are the motor areas. But despite this symphony of brain activity, people still have no conscious experience.
Scientists now believe they can explain why. With the onset of sleep, the connections between brain areas weaken and the information, though present, is not integrated. So, when a powerful magnet is used to stimulate the brain specifically in the premotor area, activity spreads to the rest of the brain when people are awake but remains locally confined when they are asleep.
A similar uncoupling could explain how anaesthetics work. Recent studies suggest that neural activity does not stop, but the brain no longer integrates information from different areas of the brain.Lead image:
MRC Toxicology Unit/Wellcome Images CC BY NC ND