Following last year’s numerous forays into the complex and often jarring world of the thinking mind, adventures in neuroscience are set to get even weirder with a new Virginia Tech study in which researchers show how ultrasound delivered to the brain can fine-tune certain cognitive abilities.
Dr. William Tyler, an assistant professor at Virginia Tech Carilion Research Institute and senior author of the study, told reporters that the research effort comes in response to previous papers outlining the role of ultrasound in neuroscience. "Ultrasound has great potential for bringing unprecedented resolution to the growing trend of mapping the human brain's connectivity," he said in a press release. "So we decided to look at the effects of ultrasound on the region of the brain responsible for processing tactile sensory inputs."
Specifically, Tyler and colleagues were determined to find out whether ultrasound can really be used to modulate the brain’s own reaction to outside stimuli. To investigate, they enrolled a number of volunteers in an experiment with ultrasound and electroencephalography (EEG) imaging technology. Immediately after stimulating a subject’s median nerve with a small electrode, the researchers delivered focused ultrasound to the area of the brain that handles information from that particular nerve. They then use the EEG data to evaluate the reaction.
As expected, the focused ultrasound suppressed the brain waves responsible for encoding the information, causing the EEG signal to weaken. To gauge the participants’ conscious response to this, they also administered two classic neurological tests: the two-point discrimination test, which measures a person’s ability to determine whether two objects touching the skin are really two distinct points; and the frequency discrimination task, in which subjects have to assess differences in frequency throughout a series of light air puffs. Both tests are designed to evaluate the brain’s ability to detect minute differences and modulations.
The team found that, although the EEG signal indicated weaker brain signals, the physical response appeared to be heightened. Intriguingly, once ultrasound was delivered to the appropriate brain area, the subjects became significantly better at both of the tasks. "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."
Mapping the Mind
Although it is not perfectly clear why a drop in brain activity leads to a more accurate physical response, the team theorizes that the temporary boost is the result of an imbalance. "It seems paradoxical, 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 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."
The current study is the latest in a growing series of efforts to enhance cognitive functions with new technology. Another example is a University of Southern California study published last year, in which researchers show that a new brain prosthesis could soon be used to enhance memory in patients with cognitive deficiencies like dementia. As our understanding of the brain’s wiring schedules becomes more and more sophisticated, scientists are constantly identifying new potential targets for this type of mind-boosting.
"Gaining a better understanding of how pulsed ultrasound affects the balance of synaptic inhibition and excitation in targeted brain regions — as well as how it influences the activity of local circuits versus long-range connections — will help us make more precise maps of the richly interconnected synaptic circuits in the human brain," first author Wynn Legon told reporters. "We hope to continue to extend the capabilities of ultrasound for noninvasively tweaking brain circuits to help us understand how the human brain works."
Source: Legon W, Sato TF, Opitz A, Tyler WJ et al. “Transcranial focused ultrasound modulates the activity of primary somatosensory cortex in humans.” Nature Neuroscience. 2014.