Are you lying? Do you have a racial bias? Is your moral compass intact?

To find out what you think or feel, we usually have to take your word for it.

But questionnaires and other explicit measures to reveal what's on your mind are imperfect: you may choose to hide your true beliefs or you may not even be aware of them.

But now there is a technology that enables us to 'read the mind' with growing accuracy: functional magnetic resonance imaging (fMRI).

Scroll down for videos

Mind-reading algorithms that use machine learning to reconstruct brain activity could reveal our innermost thoughts and could turns our society into a 'Big Brother' world

BIG BROTHER? Experts from the University of Cambridge explore the uses of mind-reading algorithms and find the technology will be successful as a lie detector - which is already being tested. These studies ask subjects to answer a series of questions that would produce both truthful answers and lies. The computer model is told which ones are which in the beginning so it gets to know your 'brain signature of lying' – the specific areas in your brain that light up when you lie, but not when you are telling the truth. Afterwards, the model has to classify new answers as truth or lies. The model is currently at a 90% accuracy rate - it gets nine out of ten correct. The next big goal: getting fMRI-based lie detection admitted as evidence in court. However, even if we can make the technology more accurate, fMRI will never be error proof. One particularly problematic topic is the one of false memories. And this also raises questions about the possibility for a 'Big Brother' future where our innermost thoughts can be routinely monitored. Advertisement

It measures brain activity indirectly by tracking changes in blood flow – making it possible for neuroscientists to observe the brain in action.

Because the technology is safe and effective, fMRI has revolutionised our understanding of the human brain.

It has shed light on areas important for speech, movement, memory and many other processes.

More recently, researchers have used fMRI for more elaborate purposes.

One of the most remarkable studies comes from Jack Gallant's lab at the University of California.

His team showed movie trailers to their volunteers and managed to reconstruct these video clipsbased on the subjects' brain activity, using a machine learning algorithm.

In this approach, the computer developed a model based on the subject's brain activity rather than being fed a pre-programmed solution by the researchers.

The model improved with practice and after having access to enough data, it was able to decode brain activity.

The reconstructed clips were blurry and the experiment involved extended training periods.

But for the first time, brain activity was decoded well enough to reconstruct such complex stimuli with impressive detail.

So what could fMRI do in the future?

This is a topic we explore in our new book Sex, Lies, and Brain Scans: How fMRI Reveals What Really Goes on in our Minds.

One exciting area is lie detection.

While early studies were mostly interested in finding the brain areas involved in telling a lie, more recent research tried to actually use the technology as a lie detector.

As a subject in these studies, you would typically have to answer a series of questions.

Technology is able to predict which are lies and which are truths 90% of the time. Meaning if it is given 10 questions it will classify answers as lies or truths nine times out of 10. This is far better than current measures such as the polygraph, which is only about 70% accurate

Some of your answers would be truthful, some would be lies.

The computer model is told which ones are which in the beginning so it gets to know your 'brain signature of lying' – the specific areas in your brain that light up when you lie, but not when you are telling the truth.

Afterwards, the model has to classify new answers as truth or lies.

The typical accuracy reported in the literature is around 90%, meaning that nine out of ten times, the computer correctly classified answers as lies or truths.

This is far better than traditional measures such as the polygraph, which is thought to be only about 70% accurate.

Some companies have now licensed the lie detection algorithms.

COMPUTER CAN TELL WHO YOU ARE THINKING ABOUT Reading minds is an ability only found in comic book heroes. But new research has revealed that computers can now analyse brain scans and work out who a person is thinking about. The AI system can even create a digital portrait of the face in question. Researchers at the Kuhl Lab at the University of Oregon used an innovative form of fMRI pattern analysis to test whether lateral parietal cortex actively represents the contents of memory. Using a large set of human face images, the first extracted latent face components, known as eigenfaces. Then machine learning algorithms were used to predict face components from fMRI activity patterns and reconstruct images of individual faces in digital portraits. Advertisement

Their next big goal: getting fMRI-based lie detection admitted as evidence in court.

They have tried several times now, but the judges have ruled that the technology is not ready for the legal setting – 90% accuracy sounds impressive, but would we want to send somebody to prison if there is a chance that they are innocent?

Even if we can make the technology more accurate, fMRI will never be error proof.

One particularly problematic topic is the one of false memories.

The scans can only reflect your beliefs, not necessarily reality.

If you falsely believe that you have committed a crime, fMRI can only confirm this belief.

We might be tempted to see brain scans as hard evidence, but they are only as good as your own memories: ultimately flawed.

Still, this raises some chilling questions about the possibility for a 'Big Brother' future where our innermost thoughts can be routinely monitored.

But for now fMRI cannot be used covertly.

There are problems with this technology because fMRI involves lying still in a big noise tube (pictured) for long periods of time. The computer model needs to get to know you and your characteristic brain activity before it can make any deductions

You cannot walk through an airport scanner and be asked to step into an interrogation room, because your thoughts were alarming to the security personnel.

Undergoing fMRI involves lying still in a big noise tube for long periods of time.

The computer model needs to get to know you and your characteristic brain activity before it can make any deductions.

In many studies, this means that subjects were being scanned for hours or in several sessions.

There's obviously no chance of doing this without your knowledge – or even against your will.

If you did not want your brain activity to be read, you could simply move in the scanner.

Even the slightest movements can make fMRI scans useless.

COULD HACKERS GET INSIDE YOUR BRAIN? Experts at the University of Washington have revealed how hackers could inserting images into dodgy apps and recording our brain's unintentional reaction using brain-computer interfaces. For example, when playing a video game users may see logos of familiar brands pop-up on the screen that just vanish. Hackers put those images in the game and they were recording your 'brain's unintentional response to them' using a BCI, which can be a wearable device that monitors stress levels or a cap covered in electrodes. This technology could one day be used by advertisers to gather more information about their customers. Also, police officers and government officials could use this method to convict criminals or as a 'remote lie detector test'. Advertisement

Although there is no immediate danger of undercover scans, fMRI can still be used unethically.

It could be used in commercial settings without appropriate guidelines.

If academic researchers want to start an fMRI study, they need to go through a thorough process, explaining the potential risks and benefits to an ethics committee.

No such guidelines exist in commercial settings.

Companies are free to buy fMRI scanners and conduct experiments with any design. They could show you traumatising scenes.

Or they might uncover thoughts that you wanted to keep to yourself.

And if your scan shows any medical abnormalities, they are not forced to tell you about it.

Mapping the brain in great detail enables us to observe sophisticated processes. Researchers are beginning to unravel the brain circuits involved in self control and morality.

Some of us may want to use this knowledge to screen for criminals or detect racial biases.

But we must keep in mind that fMRI has many limitations.

It is not a crystal ball.

We might be able to detect an implicit racial bias in you, but this cannot predict your behaviour in the real world.

MIND-READING DEVICE HELPS THOSE WITH LOCKED-IN SYNDROME SPEAK AGAIN The scientists used a technique called functional near-infrared spectroscopy (fNIRS). This involves shining long wavelength light through the scalp and measuring its absorption in the brain. At the same time, electroencephalogram (EEG) electrodes detected electrical activity. 'The machine records the blood flow... and calculates how (it) changes during 'yes' and during 'no', and the computer develops an idea, a pattern,' Birbaumer said. 'And after a while, we know what the patient is thinking, when he thinks 'yes', or when he thinks 'no', and from that we calculate the answer.' The 'known' questions elicited correct responses seven times out of 10, and the question 'Are you happy?' resulted in a consistent yes response from the four people, repeated over weeks of questioning. Advertisement

fMRI has a long way to go before we can use it to fire or incarcerate somebody.

But neuroscience is a rapidly evolving field.

With advances in clever technological and analytical developments such as machine learning, fMRI might be ready for these futuristic applications sooner than we think.

Therefore, we need to have a public discussion about these technologies now.

Should we screen for terrorists at the airport or hire only teachers and judges who do not show evidence of a racial bias?

Which applications are useful and beneficial for our society, which ones are a step too far? It is time to make up our minds.