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Bats do it, whales do it, even preying mantises do it: Ultrasound is a natural tool for navigation that scientists recently have discovered can also enhance sight and hearing in humans.

One of the realities of how the human brain works is that it is easy to disrupt things. It is easy to distract people. It is easy make people feel numb, or to fool them with optical illusions.

What isn't easy is to help people perceive the world in greater detail. But a team of researchers at the Virginia Tech Carilion Research Institute studying the functional circuitry of the human brain have done just that.

A team of scientists led by Dr. William "Jamie" Tyler, an assistant professor at the Virginia Tech Carilion Research Institute conducted a series of experiments to map the region of the brain that is responsible for tactile sensation in the hands.

To map brain activity, the scientists hooked up their volunteers to EEG (electroencephalography) machines. They placed a tiny electrode on the wrists of volunteers to stimulate the median nerve, the nerve that runs through the carpal tunnel from the arm down into the hand. Just before they sent a mild electric current through the electrode, they aimed a beam of ultrasound at the part of the brain that receives messages from the median nerve.

The scientists found that ultrasound weakened brain activity in the neurons picking up signals from the electrode. However, the researchers also found that weakened brain "waves" were accompanied by improved brain function.

The researchers performed two tests of tactile sensitivity on their volunteers. They first did a two-point discrimination test, which assesses the ability to feel the differences in the location of two pin pricks on the skin. When volunteers were zapped with ultrasound, they were able to detect smaller differences in distances between the pins that when they were not. 

Then the researchers did a test involving hit the skin with puffs of air, changing the frequency of the tiny bursts of air pressure, and asking the volunteers whether the puffs were coming more slowly, more quickly, or at the same rate. When the brain was stimulated with ultrasound, the volunteers were able to detect smaller variations in the speed of the air stream.

That the perception would be more intense when the brain appears to be less active at first baffled the brain scientists. But the Virginia Tech research team came up with an explanation of their results.

Dr. Tyler told the news site Science Daily that the results seem paradoxical, but the scientists suspected that " 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. 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."

In other words, when the brain isn't busy "talking to itself" about the events it perceives, it is able to process more information coming in from the rest of the body. But the effect of ultrasound stimulation is limited to very specific regions of the brain. When the research team moved the ultrasound beam just 10 mm to the left or right, about the width of a peanut, the effect disappeared. This means that ultrasound can be used to map the circuitry of the brain with enough precision that a neurologist or neurosurgeon could easily identify the part of the brain most involved in any sensory process.

Continue reading after recommendations

  • Virginia Tech (Virginia Polytechnic Institute and State University) (2014, January 12). Ultrasound directed to the human brain can boost sensory performance. ScienceDaily. Retrieved January 18, 2014, from http://www.sciencedaily.com­ /releases/2014/01/140112190729.htm
  • Wynn Legon, Tomokazu F Sato, Alexander Opitz, Jerel Mueller, Aaron Barbour, Amanda Williams, William J Tyler. Transcranial focused ultrasound modulates the activity of primary somatosensory cortex in humans. Nature Neuroscience, 2014. DOI: 10.1038/nn.3620
  • Photo courtesy of Anders Sandberg by Flickr : www.flickr.com/photos/arenamontanus/3473476718
  • Photo courtesy of david murphy by Flickr : www.flickr.com/photos/dabhaid/305604051

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