Farboud used a relatively new research method: a small speaker placed on the participants’ heads sent precisely targeted, inaudible sound vibrations into the brain. The technology resembles the ultrasound used to image babies in the womb. Her work shows that these vibrations can also be used to safely influence brain activity from the outside, without surgery.
In the study, participants played a computer game in which they had to look either left or right. Farboud directed ultrasound at the visual areas of the brain, giving them a subtle push. ‘When the eyes hesitated, ultrasound made the difference’, she explains. ‘We were able to adjust behaviour within a fraction of a second, purely by stimulating the brain with ultrasonic vibrations.’
She hadn’t expected the effect to be so strong. ‘When we started this research, there was no convincing evidence that ultrasound would be effective enough in humans. I ran numerous checks, and the effect proved remarkably robust.’
Farboud also measured concentrations of neurotransmitters – the chemical messengers that allow nerve cells to communicate. These levels varied widely between participants, and so did their behaviour. The ultrasonic stimulation brought everyone to a similar level, shifting them from imbalance to balance.
She stresses that this is not about controlling the brain. ‘The brain still has to do the work itself. We’re not talking about human robots, but about supporting the brain. That can open many doors.’
One of those doors may lead to new treatments for conditions such as depression or addiction. Many brain regions involved in these disorders lie too deep for current techniques to reach. Ultrasound can access them. ‘For science, this means we can now safely study deep brain areas from the outside for the first time,’ Farboud says. ‘For clinical practice, it offers the prospect of new treatments: our research shows that ultrasound can help restore balance in disrupted brain activity.’
Nature Communications
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Rapid modulation of choice behavior by ultrasound on the human frontal eye fields