Published online 7 August 2006 | Nature | doi:10.1038/news060807-3

News

Artificial electric currents guide walkers round obstacles.

Researcher Richard Fitzpatrick steers a blindfolded subject. Credit Richard Fitzpatrick

It sounds like the stuff of magic — or a Harry Potter Imperius curse. But scientists have announced that they can guide your movements by remote control. They've steered blindfolded humans around the paths of a botanical garden in Sydney, Australia, using electric currents applied just behind the walkers' ears to affect their balance and navigation. The same technique, they say, might be used in virtual-reality simulations, or to cure motion sickness.

When we walk, the researchers explain, we must both balance our body upright and steer in a given direction. To do this our brain takes in information from our eyes, ears and many other cues. The way all these work together is extremely complicated. But with a blindfold on (or when walking at night, for example), the ears are the main sensors used for balance and navigation. It's these sensors that the scientists disrupt.

The remote-control technique, called 'galvanic vestibular stimulation' (GVS), uses electrodes placed on the skin behind the ear. These stimulate our inner ear's balance (or vestibular) system, including the semicircular canals. These fluid-filled tubes sense our head moving and respond with electrical impulses to the brain, explains Stefan Glasauer, a neurologist from Ludwig-Maximilians University in Munich, Germany. Artificial electric signals created by GVS give us illusions about our head's movement.

Remote-controlled walking by GVS is not in itself new, says study co-author Richard Fitzpatrick of the Prince of Wales Medical Research Institute in Sydney. It was first demonstrated in 1999, and other researchers have studied it since. But in these earlier studies, Fitzpatrick says, "we didn't really know what was going on — the walking didn't look normal." People's balance was affected by the electrical impulses in their ears; they stumbled and stuck out their feet to save themselves from falling.

Now the researchers can steer people smoothly without making them lose their balance. There's just one snag. If you want to be guided blindfolded round obstacles by someone holding a remote control, you'll have to tilt your head back or forward. If your head is upright, the same electrical stimulus will simply make you fall over.

Side to side

This, the researchers explain, is because their electrical signals have the net virtual effect of rotating the head around an axis running from the back of the head through the nose. When one stands upright, the stimulation makes it feel as though one's head is swaying to one side or the other, as if the ears are moving towards the shoulders. The body then sways to one side to compensate, and the subject loses balance.

But when you tilt your head backwards or forwards, that rotation axis (from the back of the head through the nose) becomes vertical to the floor. Now stimulation makes it feel as though the head is rotated to point to the left or the right, and in turn the participant may feel as if they are accidentally swerving to walk in this direction. To compensate, they start to walk in a curve in the opposite direction.

This clever mechanism means the scientists can control your navigation or your balance — depending on how you tilt your head. But that dependency also limits any potential applications. As Glasauer points out, a medical patient with impaired balance might have their head in any position at any time, hampering efforts to help them with GVS. The researchers are working on changing the electric signals to remove the technique's dependency on head tilt.

Balance implants

Daniel Merfeld, of the Harvard-MIT Division of Health Sciences and Technology, is also sceptical about the practical benefits of GVS. His team is working instead on implanting electrodes inside the ear, to directly replace the semicircular canals. This would remove any confusion caused by electrical stimulation of other parts of the vestibular system, and so help the brain to properly interpret signals coming from each individual part of the ear's balance controls.

They're making progress with the system in guinea pigs. "The first human experiments are ready now in principle, though we'd need to find an appropriate subject," says Merfeld.

ADVERTISEMENT

Fitzpatrick is confident that with a bit more work, GVS could be used for flight simulation and virtual-reality games, especially with goggles creating false images for the eyes. He also suggests that the technique might be applied to cure motion sickness. "In a car, the vehicle motion could be fed back as a stimulus to cancel the vestibular signal, much in the way that noise-cancelling headphones work." At the moment, he admits, the electrical stimulation can only cause motion sickness, not cure it.

Visit our humanssteered_by.html">newsblog to read and post comments about this story.