I’m sitting in a Sussex cottage, wearing a rubber swimming cap dotted with wires and electrodes. On a laptop in front of me, a constantly shifting wash of coloured graphics portrays the activity in my brain. It’s a neat party trick, but it is also a Pandora’s box: across the world, scientists are using this kind of technology to prise open our minds, to fathom our voting preferences, our guilty thoughts, our shopping desires, even the words we are thinking. Already their activities are stealthily changing our world.

I’m the guest of Dr David Lewis, a British neuropsychologist who uses electronic brain-scanning to help brands see which of their marketing strategies best snare our interest. His Sussex University-based company, the Mind Lab, uses equipment that monitors electrical activity in the brain, and is currently investigating how to refine people’s enjoyment of video games. This is definitely the least contentious end of the market.

Amid all the scientific gadgetry and research, sceptics argue that brain-reading systems are not yet sufficiently developed to be of real use in any field. But in fact, that doesn’t matter: the prospects are far too tantalising. Companies are already marketing the technology as a way to penetrate the last frontier of exploration – the space between our ears. Lawyers, military chiefs, advertisers and politicians are eagerly buying. Welcome to the world of brainjacking, where science fiction is happening now.

Last spring, for example, an Indian court found a young woman guilty of murder based, in part, on evidence of “guilty knowledge” revealed by her brain waves. Aditi Sharma, 24, a Pune-based MBA student, was interrogated while wearing an electroencephalogram (EEG) cap similar to the one I used. It monitored her brain activity while she heard statements that were either neutral or described the killing of her former lover. Prosecutors claimed that the “brain fingerprinting” test showed how memory areas of her brain activated when she heard incriminating details.

Although an Indian government panel of scientists says this technique, Brain Electrical Oscillation Signature profiling (BEOS), should be ignored, its use in India is spreading. In January, Ravindra Kantrole, a Mumbai petty criminal, was convicted of being “the Beer Man”, a serial killer of seven victims, largely on brain-mapping evidence. Earlier this month, two priests and a nun were freed on bail in a murder case after BEOS tests showed “no memory of the killing”.

Having your brain electronically scanned is not in itself the most encouraging experience. On Dr Lewis’s screen, my inner world resembles nothing more intelligent than a duff television screen. But he says that he can use this squiggly data, along with measurements of heart rate, temperature and gaze, to gauge what is attracting my mind’s attention. That’s enough to win serious funds from media companies and car manufacturers.

Rapid developments in medical brain-imaging, most crucially in the use of functional magnetic resonance imaging (fMRI) scanners, mean that we are just starting to see much more of our mental workings. British neuroscientist John-Dylan Haynes, of the Max Planck Institute in Germany, has found how our intentions leave telltale traces in the brain. He is about to publish a study that shows how, by scanning the prefrontal cortex with an fMRI scanner, he can accurately predict in the lab what items we will want to buy.

Last year, researchers busted the brain’s “content” barrier for the first time. Scientists at Carnegie Mellon University, Pittsburgh, showed people drawings of five tools (drill, hammer, etc) and five dwellings (igloo, castle) and asked them to consider each object. A report in the journal PLoS One says that the fMRI-scanned brain patterns associated with each object were so distinctive that the computer could tell with 78 per cent accuracy which one was on a volunteer’s mind. The patterns were also remarkably similar from one person to another, so science may one day write a mind-reading dictionary that suits most people. The Pittsburgh team is now studying brain patterns that encode abstract ideas, to see if a dictionary can be written covering more complicated concepts.

Politicians are latching on to brain-scanning’s potential for spotting which of their promises attract voters’ approval. EmSense, a “neuromarketing” company founded in 2004 by seven Massachusetts Institute of Technology graduates, has developed a lightweight EEG headset resembling an Alice band that may show how wearers react to speeches and debates. The company claims it can “accurately and objectively evaluate how voters truly feel, what captures their attention and how candidates can convey their platforms in the most effective and compelling ways”.

But isn’t there a danger that such information might foster unfair bias? Justin Berenbaum, a vice president at EmSense, would not discuss the possibility, saying: “Our work in politics is confidential and we therefore cannot participate.”

The technology’s military potential is also being developed. Researchers at Honeywell Aerospace have created an EEG system that reads defence analysts’ brains as they examine spy-satellite photographs. Because our subconscious brains run significantly faster than our conscious neocortexes, a photo-analyst’s brain can unconsciously register a visual anomaly long before they may become aware of it. Honeywell’s brain scanner issues an alert when it detects neural signals that show the analyst has subconsciously noticed something suspect. Bob Smith, the company’s chief of advanced technology, claims it will make spy-photo analysis up to six times faster, “helping the military keep threats out of harm’s way”.

But most commercial attention is fixed on the premise that brain-scanning can divine truth from falsehood. Dr Steven Laken, the founder of Cephos, a company using fMRI-based lie detection, says more than 300 people have already been tested in the company’s scanner at Framingham, Massachusetts. Laken believes that American judges are on the verge of making scanning tests admissible – despite questions over their accuracy. “We tell people that the test is not 100 per cent. Studies have shown that we are between 78 and 97 per cent accurate. So long as you tell a jury that, it still can be considered as evidence.”

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