The scientists could hardly believe their eyes. 

For five years, the young man had lived in silent stillness. The doctors were convinced the motorcycle accident had left him in a vegetative state. 

Now the man, known as Patient 23, was lying in a brain scanner. Slowly, the researchers began to ask him questions. If the answer was yes, he should think of tennis. If the answer was no, he should think of walking around his house.

"Do you have any brothers?" The scanner lit up. He was thinking of tennis. It was the correct answer. Patient 23's brain was still functioning after all. 

For centuries, humans have been fascinated by the idea of being able to reach into someone else's mind and discover what they are really thinking. 

In the 1890s, after the dawn of electric lights and telephones, inventors promised that accurate mind-reading machines would be next. It was not to be. 

But now, scientists are on the brink of a breakthrough. 

In recent decades, our understanding of our thoughts has improved drastically. It was a topic that baffled Ancient Greek anatomistA biologist who studies the structure and bodies of living things, including humans.  Erasistratus, who could not comprehend where thoughts fit into the curious mass of the dissectedErisastratus cut up the brain so he could study it.  brain.

Today, using a combination of fMRIFunctional magnetic resonance imaging measures brain activity by detecting changes associated with blood flow. Blood flow is linked to the activity of neurons.  scanners and artificial intelligenceArtificial intelligence, or "AI," is the ability for a computer to think and learn. With AI, computers can perform tasks that are typically done by people, including processing language, problem-solving, and learning., researchers think they have cracked the code. Thoughts, they say, are a collection of interrelated points in a dense "meaning space". Different thoughts cause activity in neuronsNeurons, also known as nerve cells, are cells in the nervous system that use chemical or electrical signals to transmit information throughout the body.  in different areas of the brain.

New research, and new possibilities, are emerging all the time. In 2018, neuroscientists built a system that could guess the sentences that subjects were reading silently to themselves. A detailed map of the concepts in our mind could be just years away. 

But it is not just scientists who are working on mind-reading. In China, dozens of factories have started monitoring employees' brainwaves to read their emotions. This April, brain implant company NeuralinkA neurotechnology company that develops interfaces to allow a brain to operate a machine directly. released a video of a monkey playing a game with its mind.

Now, some lawmakers say the real question is not whether we can build mind-reading machines, but whether we should. 

There is no doubt: mind-reading technology could transform the lives of people like Patient 23, who cannot communicate through speech or movement. 

But it also raises serious questions about privacy and freedom of thought. "The mind - the only truly private place - has become inspectable from the outside," summarises one journalist. 

In Chile, politicians are working on a world first "neurorights" law. The bill would force scientists to register neurotechnologiesNeurotechnology involves machines that interact directly with human neurons. like medicines.

International bodies must act now, says one neurobiologist.  "We want to do something a little bit more intelligent than wait until we have a problem and then try to fix it when it's too late."

For some, regulations would be enough to ensure mind-reading machines are not used to invade the privacy of ordinary citizens. Others think the danger is too great. Mind-reading should be banned altogether. 

Absolutely, say some. Allowing governments and companies to continue developing mind-reading and maybe even mind-controlling technologies is too great a risk. Our thoughts are the one area where we have complete privacy. Losing this privacy could put freedom itself in danger. 

Of course not, say others. The possibilities are endless. In the right hands, mind-reading machines could transform thousands of lives for the better. We should not disregard the potential of an entire field of scientific discovery over as-yet-unrealised fears. Regulation, not prohibition, is the only way forward.