Can Ultrasound Alter Brain Activity?
Written By: Paphapin Pairojtanachai
June 27, 2020
Ultrasonography, or ultrasound, is widely known as a medical procedure that uses sound waves with frequencies over the range of what humans can hear to create images or sonograms of organs, tissues, blood vessels, or other structures inside a person’s body. Being a painless method that doesn’t require radiation, ultrasound is mainly used to check the growth and development of unborn babies in pregnant women as well as to look for abnormalities in many internal organs.
As it is a “tried and true” technique, scientists have been looking for an even more advanced application for ultrasound. Today, it is understood that ultrasound passes through the skull and can either boost or suppress brain activity. Nonetheless, whether or not it can reliably alter the brain’s function is unclear. If scientists can prove that ultrasonography can be safely utilized with the human brain, then there’s a definite possibility that brain disorders could be cured through ultrasound.
Currently, transcranial magnetic stimulation (TMS), which sends electrical and magnetic impulses all over the skull, has been approved by the US Food and Drug Administration (FDA) as a noninvasive tool that can regulate brain activity and treat depression, migraine, and obsessive-compulsive disorder or OCD. Electric and magnetic fields, however, cannot be directed at a particular point deep inside the brain without affecting brain tissue that is closer to the skull. The only solution that would allow TMS to penetrate into the depth of the brain is implanting a wire through surgery, which is an invasive process. What makes ultrasound different from TMS is its ability to focus — just as light is focused through a magnifying glass — on the central regions of the brain, such as the amygdala or hypothalamus. This means that with enough evidence, ultrasound could be acknowledged as a mechanism that is even better at modulating the brain than TMS is.
Still, even though the results achieved from testing the usage of ultrasound waves on animals including cats, rodents, and monkeys, are reassuring, it is a rather complicated process for researchers to discover how ultrasound impacts neural activity. This is due to the fact that the way ultrasound works is impacted by many factors involving “the timing and intensity of ultrasound pulses, and even characteristics of the targeted neurons themselves.” In addition, there is much more to be learned about ultrasonography.
One major question that researchers have on this topic concerns the interaction between sound waves and neurons. As of now, what scientists know is that at high intensities, ultrasound waves may increase in temperature and burn parts of the brain. However, even at intensities that aren’t great enough for the waves to heat up, the mechanical energy of ultrasound can exert a force that disturbs the ion channels in brain cells, thus influencing the way signaling occurs between them. Additionally, ultrasound waves may also affect receptors in glial cells, which are cells that do not fire electrical impulses but surround and support the neurons. Because of the various effects that ultrasound puts on brain cells, “it’s very hard to [develop] any unifying theory about the exact mechanism of ultrasound,” as Seung-Schik Yoo, a neuroscientist at Harvard University, says.
Even so, regardless of its mechanism, ultrasonography has been used to improve patients’ performances in cognitive and sensory tasks over the past several years. Psychiatrists and neuroscientists who have tested ultrasound report that the effects of ultrasound are much more subtle than those of TMS, and that they are confident in the safety of ultrasound in bringing clear effects to the human brain. Furthermore, with the FDA’s permission, many teams have used ultrasound waves at “intensities up to eight times as high as the limit for diagnostic ultrasound” to treat diseases such as epilepsy and chronically impaired states of consciousness. The outcome was fascinating, and there was no significant damage to brain tissues or blood vessels. Moreover, in contrast to TMS, ultrasound tremendously lowered the patients’ pain thresholds.
In the future, many scientists aim to use ultrasonography to treat other illnesses such as Alzheimer’s disease. Nevertheless, although ultrasound seems to be an exceptional tool that could possibly cure brain diseases, as Mark George, a psychiatrist at the Medical University of South Carolina, said, “Ultrasound holds that promise, but the question is can it really deliver?”
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