by Monash University

Overall response time modulations in humans and in monkeys. Credit: Brain (2024). DOI: 10.1093/brain/awae273

Brain stimulation using electrodes placed on the head has a great potential to be used in clinical practice to treat depression, anxiety and even addiction. Yet despite its widespread use in clinics and online availability for home use to improve mood and performance in various tasks, it is not clear how the therapy actually works to exert its modulatory effects on various cognitive functions.

Now, Monash researchers have studied what happens in the brain when it is being treated with Transcranial Direct Current Stimulation (tDCS), a non-invasive brain stimulation technique in which low-intensity direct currents are delivered through electrodes positioned on a person's scalp. The tDCS has a low intensity which is equivalent to the power provided by small batteries.

Associate Professor Farshad Mansouri from Monash University's Biomedicine Discovery Institute (BDI), the lead author of the study, published in the journal Brain, highlighted the significant potential of tDCS to improve cognitive and behavioral deficits in patients suffering from stroke, depression, schizophrenia and substance addiction.

Associate Professor Mansouri noted that tDCS is becoming commercially available, with growing public interest in using it for improving mood, boosting learning, and managing conditions such as overeating, gambling, and age-related cognitive decline.

"This widespread use—without truly understanding what is happening within the brain—has provoked concerns regarding the safety and efficacy of this technique, particularly because our understanding of how it affects the brain is very limited," he said.

"Our findings show how tDCS modulates both prefrontal cell activity and behavior and provide mechanistic evidence to address where, when, and how tDCS influences neuronal activity and cognitive functions."

In collaboration with Dr. Daniel Fehring and other researchers at the RIKEN Center for Brain Science in Japan and Monash BDI's Professor Marcello Rosa, the team conducted a five-year study that has finally addressed fundamental questions regarding the neuronal basis of tDCS effects on cognitive functions.

The researchers recorded the activity of individual neurons in the prefrontal cortex before, during, and after using tDCS while participants performed cognitive tasks. They found that tDCS, when applied to the prefrontal cortex, significantly influences how neurons respond to specific tasks and situations, affecting behavior as a result.

According to Associate Professor Mansouri, unlike the common belief that tDCS simply increases or decreases overall neuronal activity, "Our study showed that tDCS specifically enhances the neurons' response to certain events without altering their baseline activity.

"Additionally, tDCS reduced the variability in neuron activity while boosting task-related brain activities. Importantly, multiple tDCS sessions did not lead to any seizure-like activity," he said.

"This study marks a significant advancement in understanding the mechanistic basis of tDCS and bridges the gap between cellular-level modulations and cognitive-behavioral outcomes, paving the way for a safer and more effective application of brain stimulation techniques in research and clinical settings."

More information: Daniel J Fehring et al, Direct current stimulation modulates prefrontal cell activity and behaviour without inducing seizure-like firing, Brain (2024). DOI: 10.1093/brain/awae273

Journal information: Brain 

Provided by Monash University