Published : 23 Sep 2026, 02:11 AM
Updated : 23 Sep 2026, 02:11 AM
General anaesthetics have been used in medicine since 1846, transforming surgery by allowing patients to temporarily lose consciousness. More than 350 million operations are now performed under general anaesthesia each year, BBC reports.
Yet scientists still do not fully understand how the drugs make people unconscious -- and the mystery is offering clues about how consciousness itself works.
There are several types of anaesthetic, ranging from rarely used gases such as xenon to propofol, the most widely used general anaesthetic.
Despite their different chemical structures, they interfere with communication between nerve cells and cause a global reduction in brain activity.
But it remains unclear whether unconsciousness requires the whole brain to shut down or whether particular regions trigger the process.
Nick Franks, professor of biophysics and anaesthetics at Imperial College London, points to the thalamus, a deep-brain structure that acts as a hub between different regions. It appears to power down early under general anaesthesia and is also important in sleep and arousal.
Experiments have found that stimulating parts of the thalamus can wake anaesthetised animals, while some people in comas have also been roused through thalamic stimulation.
Other researchers believe the cerebral cortex, particularly the frontal and parietal lobes, plays a central role in consciousness, according to the BBC report.
A Possible ‘Third State’
Anaesthesia has also raised questions about whether consciousness exists on a spectrum rather than simply being on or off.
An estimated one in 15,000 patients undergoing surgery experiences accidental awareness, remembering parts of the procedure after waking.
Jaideep Pandit, a consultant anaesthetist at Oxford University Hospitals, has proposed that some patients may enter a “third state” between consciousness and unconsciousness.
In experiments, patients given an anaesthetic and muscle relaxant were able to move one hand because a tourniquet prevented the relaxant from reaching the forearm.
About one third could squeeze an experimenter's fingers on command despite showing no outward signs of being awake or experiencing pain.
Pandit says the findings suggest a level of consciousness between normal wakefulness and complete unconsciousness.
A Window into Consciousness
Scientists are also studying anaesthesia to understand why conscious experiences are unique to each individual, BBC said.
Andrea Luppi, a neuroscientist at the University of Cambridge, used functional MRI scans to examine how different brain regions communicate under anaesthesia.
Normally, patterns of brain activity are highly individual and can act almost like a fingerprint. But Luppi and his colleagues found that people's brains became less distinct from one another under anaesthesia.
The anaesthetised human brain also became more similar to the brains of other primates, suggesting that the areas most affected may include some of the brain's more recently evolved regions.
Luppi argues that a key feature of anaesthesia is the disruption of communication between distant parts of the brain.
During wakefulness, regions can interact even when they are not directly connected. Under anaesthesia, this broader communication becomes much rarer.
His findings support the idea that consciousness does not originate from a single brain region but emerges from the coordination of different networks.
Luppi has also suggested that studying anaesthesia could help explain how psychedelics such as LSD and psilocybin alter consciousness.
While anaesthetics reduce communication between brain regions, psychedelics appear to increase and diversify those connections.
The precise nature and location of consciousness, however, remain unresolved.
