Liar liar!

MRI scanners usually sit humming innocuously in a large, white walled room with a linoleum floor. Before entering this slightly sinister room, everything metallic on, or attached, to your body is removed. Once slid inside the hollow white cylinder, everyone else leaves the room while the ‘scanée’ lies waiting within the depths of the scanner.  The one time I’ve been inside a scanner I remember a metallic echoing voice asking me if I’m OK, and then the sound like a pneumatic drilling started.

This impressive, extremely expensive machine has the ability to read your brain. Well, sort of! And there are campaigners in the America who are pushing for them to be used in a court of law as a lie detector.

Understandably this is incredibly controversial. Some people believe this is an invasion of privacy, delving into the inner workings of your brain, but more importantly many people are sceptical of the accuracy of such a test.

MRI machines work by placing part of your body within an extremely powerful magnetic field. Weaker magnetic fields are then applied rapidly at different angle to the main field. This causes the nuclei of hydrogen atoms within the body’s tissues to resonate and emit faint electromagnetic signals. A detailed analysis of these signals is then assembled into phenomenally detailed images. An fMRI is simply a series of extremely rapid, less precise scans which show the change in the position of hydrogen nuclei over time, in particular where oxygenated blood is in the brain.

As the magnetic properties of haemoglobin changes whether it is carrying blood or not, it is possible to detect which brain cells are using oxygenated blood, and therefore processing information. When a person is lying, it is thought that more areas of the brain are active than usual as they grapple to put together a false story.

However, a major assumption of this principle is that every person’s brains works identically. People’s physiology is extremely varied, meaning huge samples are needed in order to reveal any sort of correlations and results. Any researcher worth their salt will immediately be sceptical at the thought of obtaining results from just one subject. In cognitive neuroscience studies a minimal sample of 30-40 people are usually scanned in order to get an average showing results.

Another concern of researchers worldwide is whether the lab based experiments are true representation of the real world. If you’ve ever been inside a MRI scanner, you’ll know it’s not entirely comfortable; it’s not the same as sitting in a room having a bit of a chinwag with someone and telling a bit of a fib!

Last year, fMRI data was used for the first time in an American court room, although not as a lie detector. The defence in a murder trial tried to use fMRI evidence to persuade the jury that their client had a mental illness. It didn’t, and the defendant was given the death penalty. Attempts have been made to use fMRI ‘lie detector’ data in court, but so far judges have thrown it out before the jury has even seen it.

Despite this, many are still convinced that one day fMRI lie detecting scans will become a reality.

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