Dhaka, Sept. 23 -- 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 unconscious...