Ultrasound directed to the brain can improve sensory perception in humans, scientists have found.
Researchers at Virginia Tech Carilion Research Institute in US found that ultrasound directed to a specific region of the brain can boost performance in sensory discrimination.
"Ultrasound has great potential for bringing unprecedented resolution to the growing trend of mapping the human brain's connectivity," said William Tyler, an assistant professor at the Virginia Tech Carilion Research Institute, who led the study.
"So we decided to look at the effects of ultrasound on the region of the brain responsible for processing tactile sensory inputs," Tyler said.
The scientists delivered focused ultrasound to an area of the cerebral cortex that corresponds to processing sensory information received from the hand.
To stimulate the median nerve - a major nerve that runs down the arm and the only one that passes through the carpal tunnel - they placed a small electrode on the wrist of human volunteers and recorded their brain responses using electroencephalography, or EEG.
Then, just before stimulating the nerve, they began delivering ultrasound to the targeted brain region.
The scientists found that the ultrasound both decreased the EEG signal and weakened the brain waves responsible for encoding tactile stimulation.
The scientists then administered two classic neurological tests: the two-point discrimination test, which measures a subject's ability to distinguish whether two nearby objects touching the skin are truly two distinct points, rather than one; and the frequency discrimination task, a test that measures sensitivity to the frequency of a chain of air puffs.
The subjects receiving ultrasound showed significant improvements in their ability to distinguish pins at closer distances and to discriminate small frequency differences between successive air puffs.
"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 neighbouring neurons within the cerebral cortex," Tyler said.
"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," he said.
To understand how well they could pinpoint the effect, the research team moved the acoustic beam one centimetre in either direction of the original site of brain stimulation - 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. This finding represents a new way of noninvasively modulating human brain activity with a better spatial resolution than anything currently available," Tyler said.
