Walking upright separates humans from most other creatures. Our bipedal gait is a wonder of balance but it remains unclear exactly how our brains manage to maintain this posture and use it to arrive at desired destinations. Now researchers have shown that the balance mechanisms of our inner ears play a decisive role in directing the human walk, as well as demonstrating that blindfolded volunteers can be steered by simple electrical current.

Richard Fitzpatrick of the University of New South Wales in Australia and his colleagues gathered five men and five women and set them on a path. After staring at a target six meters (20 feet) away, the subjects were blindfolded and the researchers began running a slight electrical current through electrodes placed behind their ears. The current disrupted the constant electrical signaling produced by the sensory hair cells in the three canals of the inner ear. (They fire 90 times a second when the head is at rest.) Their continuous firing rate tells the brain exactly how the head is moving, which the brain then uses to maintain balance and direction.

But when that signaling is disrupted, either by increasing or decreasing its rate, walking chaos ensues. The researchers could drive the subject to either the right or left depending on the direction of the current, basically convincing the brain that the head was rotating in a given direction and forcing it to make concomitant adjustments in the direction of the walk in order to arrive at the now misperceived goal. Further, if the researchers asked the subjects to tilt their heads forward toward the ground or backward toward the sky they would veer off course by an even greater degree. And when subjects held their heads only slightly back, the current completely disrupted their balance, inducing swaying and stumbling.

The research shows that the human walk depends on the accuracy of the signals of these tiny hair cells in the ear. Further experiments in the Sydney Botanic Gardens proved that researchers could guide a blindfolded subject through its meandering pathways via electrical cues alone. "By manually adjusting the stimulus intensity and polarity we could, by remote radio control, steer freely walking subjects so that they kept to the paths and avoided obstacles for periods of many minutes," the team writes in the paper presenting the research in this week's Current Biology. "Stimulation techniques developed from those that we used here will provide a fundamental understanding of the processes of spatial representation and transformation in the brain and thus lead the way to diagnostic, therapeutic and virtual-reality applications."