Ultrasound may improve sensory perception, according to a new study in humans.
By directing ultrasound to a specific brain area, researchers were able to improve people's ability to discriminate between sensory inputs. Ultrasound is sound far above the upper limit of what humans can hear. It's useful in medical imaging. Doctors and technicians send bursts of ultrasound through tissue and record the echoes, creating a picture of what's inside — whether it's an injured knee or a fetus in utero.
Ultrasound also has potential for mapping the connectivity of the brain. Neuroscientists are particularly interested in understanding how brain areas chat with one another; in fact, a new federal project, the BRAIN Initiative, has the goal of mapping the healthy human brain. (Inside the Brain: A Photo Journey Through Time)
Ultrasound is one of several noninvasive methods that stimulate the brain. Another is transcranial magnetic stimulation, which stimulates the brain with magnets. A third is transcranial direct current stimulation, which uses electrodes to deliver a weak electrical current to the brain through the scalp.
The new study suggests that ultrasound may be the best of the bunch.
"We can use ultrasound to target an area of the brain as small as the size of an M&M," study researcher William Tyler, a neuroscientist at the Virginia Tech Carilion Research Institute, said in a statement. "This finding represents a new way of noninvasively modulating human brain activity with a better spatial resolution than anything currently available."
Tyler and his colleagues focused on sensory perception from the hand. They first placed an electrode on the wrist, over the nerve that carries impulses from the hand to the brain. Using a small electrical current, they stimulated that nerve while focusing ultrasound on the brain region that processes the nerve's signals.
The researchers recorded the participants' brain responses with electroencephalography (EEG), electrodes on the scalp that measure the electrical activity of the brain. The ultrasound weakened the brain waves that encode the tactile stimulation, they found.
But the next set of experiments revealed something truly strange.