Non-invasive deep brain stimulation may help to treat depression and addiction

A new technique known as non-invasive deep brain stimulation may be able to treat mental health conditions such as depression, OCD and addiction, according to a group of Swiss researchers.

The research, led by Friedhelm Hummel, Defitchech Chair of Clinical Neuroengineering at the Ecole Polytechnique Fédérale de Lausanne, uses transcranial Temporal Interference Electric Stimulation (tTIS) to target regions deep in the brain. These regions control several important cognitive functions and are involved in different neurological and psychiatric conditions.

“Invasive deep brain stimulation (DBS) has already successfully been applied to the deeply seated neural control centres in order to curb addiction and treat Parkinson, OCD or depression,” Hummel said. “The key difference with our approach is that it is non-invasive, meaning that we use low-level electrical stimulation on the scalp to target these regions.”

Pierre Vassiliadis, a postdoctoral researcher at the Université catholique de Louvain, and lead author of the study, published in Nature Human Behaviour, said that tTIS uses two pairs of electrodes attached to the scalp to apply weak electrical fields inside the brain: “Up until now, we couldn’t specifically target these regions with non-invasive techniques, as the low-level electrical fields would stimulate all the regions between the skull and the deeper zones—rendering any treatments ineffective. This approach allows us to selectively stimulate deep brain regions that are important in neuropsychiatric disorders.”

Real-time information about success or failure

The technique was initially tested in rodents before being applied to humans.  In the study, 24 people performed a task in an MRI scanner while experiencing the deep-brain stimulation. The task involved tracking a moving target, and participants were given real-time information about their success or failure throughout the trial to see if the stimulation disrupted the participants’ ability to learn through reinforcement.

Using the technique, the researchers set one pair of electrodes to a frequency of 2,000 Hz and the other to to 2,080 Hz. Detailed computational models of the brain structure enable the researchers to position the electrodes are on the scalp to allow their signals to intersect in the target region.

It is at this intersection that the intervention works. The small frequency disparity of 80 Hz between the two currents becomes the effective stimulation frequency within the target zone. The high base frequencies do not stimulate neural activity directly, leaving the intervening brain tissue unaffected and focusing the effect solely on the targeted region. In the latest research, the target zone was the striatum, which plays a role in reward and reinforcement.

“We’re examining how reinforcement learning, essentially how we learn through rewards, can be influenced by targeting specific brain frequencies,” Vassiliadis said.

By stimulating the striatum at 80 Hz, the researchers found they could disrupt its normal functioning, directly affecting the learning process.

Because reward mechanisms play an important part in conditions such as addiction and depression, the ability to target the striatum could allow doctors to treat those conditions by reducing the association between, for example, an addictive substance and the sense of reward.

“In addiction, for example, people tend to over-approach rewards. Our method could help reduce this pathological overemphasis,” said Vassiliadis.

Enhancing brain function

The research team is also exploring how different stimulation patterns can not only disrupt but also enhance brain functions.

“This first step was to prove the hypothesis of 80 Hz affecting the striatum, and we did it by disrupting it’s functioning. Our research also shows promise in improving motor behavior and increasing striatum activity, particularly in older adults with reduced learning abilities,” Vassiliadis said.

Hummel said he saw the approach as the beginning of a new chapter in brain stimulation, offering personalised treatment with less invasive methods: “We’re looking at a non-invasive approach that allows us to experiment and personalise treatment for deep brain stimulation in the early stages.”.

Another key advantage of tTIS is that it has minimal side effects, with most participants reporting only mild sensations on the skin.