Ultrasound Sharpens Human Sensory Perception

Low-intensity transcranial ultrasound can heighten sensory perception in humans, according to a paper published online January 12 in Nature Neuroscience. In the study, carried out by scientists at the Virginia Polytechnic Institute and State University's (Virginia Tech; Roanoke, VA) Carilion Research Institute, subjects receiving ultrasound showed significant improvements in their ability to perform on two classic neurological tests, the two-point discrimination test, and the frequency discrimination test.

A release published on the Virginia Tech Web site quotes study leader William "Jamie" Tyler, assistant professor at the Carilion Research Institute, as saying,"Ultrasound has great potential for bringing unprecedented resolution to the growing trend of mapping the human brain's connectivity. So we decided to look at the effects of ultrasound on the region of the brain responsible for processing tactile sensory inputs."

The team delivered focused ultrasound to an area of the cerebral cortex that processes sensory information received from the hand. They placed small electrodes on the wrists of volunteers and used an electroencephalography (EEG) machine to record their brain waves. The scientists found that the ultrasound both decreased the EEG signal and weakened the brain waves responsible for encoding tactile stimulation. Oddly, these effects had the result of actually heightening the subjects' performance on the tests.

"Our observations surprised us," said Tyler. "Even though the brain waves associated with the tactile stimulation had weakened, people actually got better at detecting differences in sensations. It seems paradoxical, but we suspect that the particular ultrasound waveform we used in the study alters the balance of synaptic inhibition and excitation between neighboring neurons within the cerebral cortex," Tyler continued. "We believe focused ultrasound changed the balance of ongoing excitation and inhibition processing sensory stimuli in the brain region targeted and that this shift prevented the spatial spread of excitation in response to stimuli, resulting in a functional improvement in perception."

The research team then moved the ultrasound beam 1 cm to one side, then the other, of the original stimulation site and the effect disappeared. "That means we can use ultrasound to target an area of the brain as small as the size of an M&M," Tyler said. "This finding represents a new way of noninvasively modulating human brain activity with a better spatial resolution than anything currently available." Based on these and previous findings, the researchers have concluded that ultrasound has finer spatial resolution than two other noninvasive brain stimulation technologies, magnetic stimulation and direct current stimulation, which uses weak electrical currents delivered directly to the brain.

"In neuroscience, it's easy to disrupt things," said Tyler. "We can distract you, make you feel numb, trick you with optical illusions. It's easy to make things worse, but it's hard to make them better. These findings make us believe we're on the right path."