Researchers from the University of Manchester have presented a video at the European Anesthesiology Conference that demonstrates how a brain slowly loses consciousness when undergoing a propofol induction. Using an instrument called a functional electrical impedence tomography by evoked response (fEITER), they were able to visualize the brain slipping into sleep in real time. Dr. Brian Pollard, the presenter of the paper at the conference, noted that initially propofol inhibits the inhibitory neurons in the brain. The brain thus becomes more excitable, which is seen on the video.Then as more propofol is given, the excitatory neurons are also inhibited and the brain then slips into unconsciousness. Unlike what patient's may say they feel, the brain doesn't become anesthetized like a light switch. There is a gradual decline in the brain function.
I have noticed the same phenomenon when anesthetizing patients. If one pushes propofol very quickly, the brain goes through its stages of sleep rapidly. Therefore it appears the patient is out "like a light." However if you give the propofol slowly, in small boluses, many patients lose their inhibition first. This is manifested as a sudden need to vocalize their thoughts or express their emotions. Many patients are very anxious and quiet as they are about to go to sleep. But once the propofol is started, they will start talking about almost anything, including how attractive their doctors or nurses are. We don't hold it against them though. We know it's just a drug induced euphoria and the patient will have no recollection of it after the surgery.Now we have scientific visual evidence of this state.