Does transcranial direct current stimulation improve speech production in patients with speech impairment after stroke?

This study evaluated the effectiveness of transcranial direct current stimulation (tDCS) on speech intelligibility, and speech-related physiological and vocal functions in dysarthric (speech impairment) patients after stroke. The data showed that tDCS enhanced the effects of traditional speech therapy in these patients.

A stroke happens when the blood flow to the brain is cut-off. The brain cells stop receiving oxygen and begin to die. This leaves patients with various side effects, such as dysarthria. This disorder consists of impairment in language. Dysarthria is a motor speech disorder in which the muscles that are used to produce speech are damaged, paralyzed, or weakened.

Transcranial direct stimulation (tDCS) is a type of non-invasive brain stimulation technique that modifies the brain’s plasticity. This technique applies a weak electrical current from two small electrodes on the head for 10 – 20 minutes. Anodal tDCS makes brain regions more active, while cathodal tDCS makes brain regions less active. Prior studies showed that tDCS improves body function, gait, and movement. However, the effectiveness of tDCS on speech intelligibility, and speech-related physiological and vocal functions in dysarthric patients after stroke is still unknown.

This study involved 9 patients with dysarthria after a stroke. Patients were randomly assigned into two groups. Group 1 included 5 patients who received 2mA of anodal tDCS in the left part of the brain for 15 minutes. Group 2 included 4 patients who received a sham procedure (control) for 30 seconds. Both groups also received 15 minutes of speech therapy.

Both groups had improved speech intelligibility at the word level, reduced short rushes of speech during passage reading, and improved speech rate.

Patients in group 1 showed significant improvement in the movements required for speech production and syllable production in sentences compared to patients in group 2. Patients in group 1 showed reduced changes in voice amplitude compared to patients in group 2.

This study concluded that tDCS enhanced the effects of traditional speech therapy on speech intelligibility, and speech-related physiological and vocal functions in dysarthric patients after stroke.

The sample size was very small and only included 9 patients. The patients had different degrees of dysarthria ranging from mild to severe. Further larger studies are needed to validate the findings.