At a laboratory in Germany, volunteers slide into a donut-shaped MRI machine and perform simple tasks, such as deciding whether to add or subtract two numbers, or choosing which of two buttons to press.

They have no inkling that scientists in the next room are trying to read their minds - using a brain scan to figure out their intention before it is turned into action.

In the past, scientists had been able to detect decisions about making physical movements before those movements appeared. But researchers at Berlin’s Bernstein Center for Computational Neuroscience claim they have now, for the first time, identified people’s decisions about how they would later do a high-level mental activity - in this case, adding versus subtracting.

While still in its initial stages, the techniques may eventually have wide-ranging implications for everything from criminal interrogations to airline security checks. And that alarms some ethicists who fear the technology could one day be abused by authorities, marketers, or employers.