Whales, bats, and even praying mantises¹ use ultrasound as a sensory² guidance system -- and now a new study has found that ultrasound can modulate³（调节） brain activity to heighten sensory perception in humans. Virginia Tech Carilion Research Institute scientists have demonstrated that ultrasound directed to a specific region of the brain can boost performance in sensory discrimination. The study, published online Jan. 12 in Nature Neuroscience, provides the first demonstration⁴ that low-intensity, transcranial（经颅的）-focused ultrasound can modulate human brain activity to enhance perception.

 

"Ultrasound has great potential for bringing unprecedented⁵ resolution to the growing trend of mapping the human brain's connectivity," said William "Jamie" Tyler, an assistant professor at the Virginia Tech Carilion Research Institute, who led the study. "So we decided⁶ to look at the effects of ultrasound on the region of the brain responsible for processing tactile⁷ sensory inputs⁸."

 

The scientists delivered focused ultrasound to an area of the cerebral⁹ cortex that processes sensory information received from the hand. To stimulate¹⁰ the median nerve -- a major nerve that runs down the arm and the only one that passes through the carpal（腕骨的） tunnel -- they placed a small electrode on the wrist of human volunteers and recorded their brain responses using electroencephalography, or EEG. Then, just before stimulating¹¹ 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 stimulation¹².

 

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 touching¹³ 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 puffs¹⁴.

 

What the scientists found was unexpected.

 

The subjects receiving ultrasound showed significant improvements in their ability to distinguish pins at closer distances and to discriminate¹⁵ small frequency differences between successive air puffs.

 

"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."

 

Why would suppression of brain responses to sensory stimulation heighten perception? Tyler speculates that the ultrasound affected¹⁶ an important neurological balance.

 

"It seems paradoxical（矛盾的）, 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 said. "We believe focused ultrasound changed the balance of ongoing¹⁷ excitation and inhibition processing sensory stimuli¹⁸ in the brain region targeted and that this shift prevented the spatial¹⁹ spread of excitation in response to stimuli resulting in a functional²⁰ improvement in perception."

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