In a twist on nontraditional uses of ultrasound, a group of neuroscientists at Arizona State University (ASU) has developed pulsed ultrasound techniques that can remotely stimulate brain circuit activity, according to a study published in the Oct. 29 issue of PLoS One.
The researchers said that their findings provide insight into how low-power ultrasound can be harnessed for the noninvasive neurostimulation of brain circuits and offers the potential for new treatments of brain disorders and disease.
“We were able to unravel how ultrasound can stimulate the electrical activity of neurons by optically monitoring the activity of neuronal circuits, while we simultaneously propagated low-intensity, low-frequency ultrasound [LILFU] through brain tissues," said lead investigator William Tyler, assistant professor of neurobiology and bioimaging in the ASU School of Life Sciences in the College of Liberal Arts and Sciences in Phoenix.
The research group discovered that remotely delivered LILFU increased the activity of voltage-gated sodium and calcium channels in a manner sufficient to trigger action potentials and the release of neurotransmitter from synapses. Since the processes are fundamental to the transfer of information among neurons, the authors suggested that this type of ultrasound could provide a powerful new tool for modulating the activity of neural circuits.
"Many of the stimulation methods used by neuroscientists require the use and implantation of stimulating electrodes, requiring direct contact with nervous tissue or the introduction of exogenous proteins, such as those used for the light-activation of neurons," Tyler explained.
“We were quite surprised to find that ultrasound at power levels lower than those typically used in routine diagnostic medical imaging procedures could produce an increase in the activity of neurons while higher power levels produced very little effect on their activity," Tyler says.
Other neuroscientists and engineers have also been developing new neurostimulation methods for controlling nervous system activity, and several approaches show promise for the treatment of a variety of nervous system disorders. For example, deep brain stimulation and vagal nerve stimulation have been shown to be effective in managing psychiatric disorders such as depression, post-traumatic stress disorder and drug addition, as well as for therapies of neurological diseases, such as Parkinson's disease, Alzheimer's disease, Tourette Syndrome, epilepsy, dystonia, stuttering, tinnitus, recovery of cognitive and motor function following stroke and chronic pain.
However, these therapies still pose risks to patients because they require the surgical implantation of stimulating electrodes. Thus, they are often only available to patients presenting the worst of prognoses, according to the researchers.
The acoustic frequencies utilized by Tyler and his colleagues to construct their pulsed ultrasound waveforms, overlap with a frequency range where optimal energy gains are achieved between transcranial transmission and brain absorption of ultrasound—which allows the ultrasound to penetrate bone and yet prevent damage to the soft tissues, according to the researchers.