Mild electrical brain stimulation—specifically, transcranial direct current stimulation (tDCS)—did not further improve motor recovery in stroke survivors in a multicentre study presented as late-breaking science at the 2025 International Stroke Conference (ISC; 5–7 February, Los Angeles, USA).
“The results are somewhat surprising to us,” said Wayne Feng (Duke University School of Medicine, Durham, USA), who led the study alongside co-principal investigator Gottfried Schlaug (University of Massachusetts Chan Medical School, Worcester, USA). “We initially hoped that a higher dose at four milliamps of electrical stimulation had a better effect than a lower dose as well as the sham group, but we did not see that.”
Depending on the part of the brain that is affected, a stroke may impair arm and/or leg movement and activities of daily life among survivors, and motor impairment—characterised by arm and/or leg weakness—is the most common complication after stroke.
Constraint-induced movement therapy (CIMT), which restricts movement of a patient’s unaffected arm, forcing them to use their stroke-affected side, has been shown to improve motor function and quality of life in certain stroke patients with preserved hand movement. However, it is an intensive treatment typically carrying a significant time burden, which can be challenging for stroke survivors, according to Feng.
In the present study, dubbed ‘TRANSPORT 2’, researchers assessed whether tDCS—involving up to four milliamps, powered by a nine-volt battery, being delivered through the skull—could enhance the effects of CIMT, allowing for better use of the arm affected by a patient’s stroke.
They evaluated three aspects of arm function (motor impairment [Fugl-Myer upper-extremity scale], function [Wolf motor functional test] and quality of life [stroke impact scale hand subscale]) after 10 sessions, over a two-week period, in 129 ischaemic stroke survivors (42% women; average age, 59 years) who were undergoing CIMT across 15 US medical centres. These patients were randomly assigned to be treated with one of three doses of electrical stimulation: sham/placebo stimulation; low-dose stimulation (two milliamps); and higher-dose stimulation (four milliamps). The stimulation treatments were administered for 30 minutes while each session of CIMT lasted 120 minutes.
The analysis found that tDCS up to four milliamps did not amplify the effect of CIMT. While stroke survivors in all three groups improved after two weeks of treatment, and the effect continued at one month and three months after the intervention, the magnitude of improvement among the three groups was similar. The researchers concluded that electrical stimulation was found to be safe and tolerable in stroke patients, adding that it appeared feasible to implement the combined intervention involving brain stimulation plus intensive rehabilitation therapy in a multicentre clinical trial setting.
One limitation of the study is a trend of uneven representation of women in each group—something that the investigators deem relevant due to the fact that women may respond differently to brain stimulation compared with men. Another limitation is that the study was interrupted by the COVID-19 pandemic, which slowed enrolment and created scoring issues relating to the primary outcomes.
“In future clinical trials, we plan to enhance our approach by implementing several improvements,” Feng said. “These improvements will include using a higher dose—more than four milliamps—ensuring men and women are equally distributed in each group, and ensuring consistent administration and scoring of the primary outcomes across all clinical trial sites. It may take us a few attempts before we achieve success.”
The Phase 2 TRANSPORT 2 study is described in an American Heart Association press release as the first funded, multicentre stroke recovery study on the National Institutes of Health (NIH) StrokeNet—a network of US regional centres and hospitals conducting major stroke-related clinical trials with a focus on acute treatment, prevention, and recovery.
