Source: Herpich et al., JNeurosci (2019)

For decades, neuroscientists have experimented with various non-invasive transcranial stimulation techniques that send electrical currents to a targeted brain area through the skull. There are four widely studied methods of transcranial electrical stimulation (tES) that can induce neuroplasticity within the human brain. Transcranial random noise stimulation (tRNS) is one non-invasive brain stimulation technique that is making headlines this week.

Transcranial random noise stimulation (tRNS) may enhance visual learning speed and retention in healthy adults and patients with brain damage, according to a study published May 27 in the Journal of Neuroscience. For the first time, this paper, "Boosting Learning Efficacy with Non-Invasive Brain Stimulation in Intact and Brain-Damaged Humans," reports evidence that brief periods of computer-based visual training coupled with tRNS over the visual cortex resulted in dramatic improvements to visual motion perception.

In the paper's abstract, the authors sum up the significance of their findings:

"Here, we show for the first time in female and male human participants that just 10 days of visual training coupled with transcranial random noise stimulation (tRNS) over visual areas causes dramatic improvements in visual motion perception. Relative to control conditions and anodal stimulation, tRNS-enhanced learning was at least twice as fast, and, crucially, it persisted for 6 months after the end of training and stimulation."

Source: The Database Center for Life Science/Wikimedia Commons

During tRNS, an alternating electrical current with a broad oscillation spectrum—that continually changes frequency (ranging from 0.1 to 640 Hz)—is applied externally to a specific brain region. For their most recent study on visual learning, Herpich et al. targeted the visual cortex.

In 2008, tRNS was first used on humans by Daniella Terney and colleagues at öttingen University (Terney et al., 2008). The main goal of the latest tRNS research (2019) was to corroborate a growing body of evidence suggesting that non-invasive brain stimulation is a safe and painless way to speed up specific types of learning.

For this study, researchers in the Tadin Lab of Vision and Cognitive Neuroscience at the University of Rochester collaborated with scientists at the Italian Institute of Technology led by Lorella Battelli, who is also an assistant professor of neurology at Harvard Medical School.

To test if tRNS could speed up visual perceptual learning in a controlled laboratory, the researchers had study participants engage with a computer-based task that involved determining the direction of different cloud-like formations of dots crawling slowly across the screen. This task measures someone's motion integration threshold, which is key to avoiding collisions with moving objects in the real world.

"All groups of participants got better at the dot motion task with practice, but the group that also trained with tRNS improved twice as much and was able to learn the motion task better than other groups. This fast improvement is something we've never seen in this patient population," co-author Duje Tadin, a professor of brain and cognitive sciences at the University of Rochester, said in a statement.

"The beauty of this combined is the very short training," Battelli said in a statement. "When you work with stroke patients you quickly realize that there is a lot of fluctuation in their ability to stay on task. Thus, training that is short and effective is a big advantage."

While this two-pronged approach could lead to more effective therapies in the future, the researchers still aren't exactly sure how and why tRNS works. "That will be the focus of future research," Tadin said. "It appears that tRNS helps put the brain in a more plastic state, which makes it more amenable to training-induced change, or learning. What we hope to learn with future work is why this happens."