Neuropeptide receptors in the brain

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:

Confocal image of normal brain tissue from the thalamus stained with antibodies to receptors for orexin (stained green). Orexins are molecules that help keep us awake and alert. They are produced in the hypothalamus and act through their receptors located in the nuclei of cells in many different parts of the brain. The red stain highlights the neurofilaments and the blue stain the nuclei.

MRC Toxicology Unit/Wellcome Images CC BY NC ND

About this resource

This resource was first published in ‘Thinking’ in September 2006 and reviewed and updated in August 2014.

Neuroscience, Psychology, Medicine
Education levels:
16–19, Continuing professional development