The reason some people feel groggy after waking from general anaesthetic may be explained by new research.
And the new understanding of the complex ways in which general anaesthetics act on the brain could eventually lead to improved drugs for surgery, according to scientists.
The study discovered how anesthetics do more than simply put patients to sleep.
Until now it had remained unclear how general anaesthesia works, even though it is one of the most common medical procedures.
Associate Professor Bruno van Swinderen, of Queensland University in Australia, said his team had overturned previous understanding of what general anaesthetics do to the brain, finding the drugs did much more than induce sleep.
He said: "We looked at the effects of propofol - one of the most common general anaesthetic drugs used during surgery - on synaptic release."
Nervous systemProf van Swinderen explained that synaptic release is the mechanism by which neurons - or nerve cells - communicate with each other.He said: "We know from previous research that general anaesthetics including propofol act on sleep systems in the brain, much like a sleeping pill.
"But our study found that propofol also disrupts presynaptic mechanisms, probably affecting communication between neurons across the entire brain in a systematic way that differs from just being asleep.
"In this way it is very different than a sleeping pill."
Adekunle Bademosi, a PhD student, said the discovery shed new light on how general anaesthetics worked on the brain.
He said: "We found that propofol restricts the movement of a key protein, syntaxin1A, required at the
synapses of all neurons. This restriction leads to decreased communication between neurons in the brain."Dazed and confused
Prof van Swinderen said the finding contributed to understanding how general anaesthetics worked, and could explain why people experienced grogginess and disorientation after coming out of surgery.He said: "We think that widespread disruption to synaptic connectivity - the brain's communication pathways - is what makes surgery possible, although effective anaesthetics such as propofol do put you to sleep first.
"The discovery has implications for people whose brain connectivity is vulnerable, for example in children whose brains are still developing or for people with Alzheimer's or Parkinson's disease.
"It has never been understood why general anaesthesia is sometimes problematic for the very young and the old. This newly discovered mechanism may be a reason."
Prof van Swinderen said more research was needed to determine if general anaesthetics had any lasting effects in the vulnerable groups of people.
He added: "Studying these effects in model systems such as rats and flies allows us to address these questions by manipulating the likely mechanisms involved, which we can't do in humans."
The research was published in the journal Cell Reports.