Brain implants that deliver electric pulses can ease depression in people who aren't responding to psychiatric drugs, a new study says.

Half of a small group of people who received brain implants experienced significant improvement in their depression symptoms, researchers reported Nov. 18 in the journal Nature Communications.

Further, more than one-third wound up virtually depression-free following the treatment, which is called deep brain stimulation.

“Deep brain stimulation shows real promise at tackling treatment-resistant depression, which can have a huge impact on people’s lives,” senior researcher Dr. Valerie Voon, a professor of neuropsychiatry and neuromodulation at the University of Cambridge in the UK, said in a news release.

Deep brain stimulation involves inserting electrodes deep into a person’s brain, where they transmit mild electrical pulses. It’s being used to treat a range of neurological conditions, most successfully among people with Parkinson’s disease, researchers said in background notes.

This is one of the largest studies to show that deep stimulation of specific brain regions can treat depression, said researcher Dr. Bomin Sun, a neurosurgeon at Shanghai Jiao Tong University School of Medicine in China.

“This study not only tells us how the brain is impaired in depression, it also highlights potential of DBS for depression,” Sun said in a news release.

For the new study, researchers recruited 26 patients in China with treatment-resistant depression and implanted electrodes to provide stimulation to two areas of the brain:

• The bed nucleus of the stria terminalis (BNST), a part of the amygdala involved in regulating stress, anxiety and fear.

• The nucleus accumbens, a key area for motivation, pleasure and reinforcement.

Half of the patients — 13 out of 26 — saw significant improvement in symptoms related to depression and anxiety, results show.

In fact, nine of the patients (35%) achieved a near-complete elimination of their symptoms, researchers said.

Researchers found that brain activity at a specific electrical frequency, called “theta activity,” corresponded to a person’s depression.

People with high levels of theta activity in the BNST tended to have worse depression and anxiety.

During the trial, researchers used stimulation to reduce theta activity in the BNST, and the pulses tracked with improvements in patients’ depression and anxiety.

“We found that brain activity at a particular frequency — theta brainwaves — could tell us which patients would have the best response to deep brain stimulation treatment in the BNST brain region,” lead investigator Linbin Wang, a research associate at the University of Cambridge, said in a news release. “This could help us personalize treatment for individual patients in future.”

“Because theta activity tracks anxiety states in real time, it means that if activity is high, we can say ‘OK, this person is an anxious state, we need to turn up stimulation’. Likewise, if theta activity is low, we can turn down the stimulation,” Voon added.