A new study finds that using ultrasound to target specific areas of the brain causes functional changes that last up to an hour. These findings pave the way for the development of non-invasive methods to treat mental illnesses such as depression and anxiety.
Typically, ultrasound examines the internal structures of the body by emitting diffuse sound waves and recording reflected sound, or echoes, to produce images. However, low-intensity transcranial ultrasound stimulation (TUS) can target both superficial and deep areas of the brain with extremely high specificity, placing ultrasound pressure on areas of the brain that change the way neurons interact.
Researchers at the University of Plymouth in the UK led a study to test the effects of TUS on brain function and found that it produced significant changes.
They recruited 24 healthy adults to study how TUS affects gamma-aminobutyric acid (GABA) levels and connections between brain regions. GABA is the main inhibitory neurotransmitter in the brain, reducing the ability of neurons to send and receive chemical messages. Specifically, GABA affects the body's response to feelings of anxiety, fear, and stress.
All participants completed three Theta-burstTUS treatments and underwent MRI after each treatment to assess changes in brain function. Theta-burstTUS is a high-frequency, short-pulse brain stimulation that closely mimics the natural rhythm of neuronal activity. It is thought to promote plasticity, the brain's ability to form and reorganize neural connections based on learning or experience.
The researchers found that TUS acting on the posterior cingulate cortex (PCC) - a deep brain region associated with emotion and memory - reduced GABA levels in the area within an hour of treatment. They also found that the way the PCC communicates with the rest of the brain (functional connectivity) improved during this time. PCC abnormalities have been found in a range of psychiatric disorders.
When TUS was applied to the dorsal anterior cingulate cortex (dACC)—a region associated with emotion, empathy, impulse control, and decision-making and, like the PCC, also implicated in psychopathology—the researchers did not see the same decrease in GABA levels, but they did see an increase in functional connectivity.
The researchers say their results show that TUS is effective in humans and can produce reversible changes in the brain. While further research is needed, they say this is a first step in developing non-invasive means of treating mental health conditions.
Elsa Fouragnan, corresponding author of the study, said: "For example, if you take a drug to treat depression, the drug affects the entire brain, and clinicians have very limited control over where the drug goes and what it does. We already know that in some cases, specific areas of the brain (and some of its connections) become dysfunctional, but other areas work well. This study gives us real potential to consider using ultrasound for more targeted interventions in people with a range of mental health problems."
Researchers are already exploring whether TUS can be used to alter the brain's dopaminergic system, the primary reward pathway that detects and interprets rewarding stimuli such as food, sex, and drugs of abuse.
The research was published in the journal Nature Communications.