Neurostimulation for the Treatment of Post-Stroke Aphasia

The aim of the trial is to determine whether 75Hz transcranial alternating current stimulation (tACS) synchronized with therapeutic linguistic tasks is an effective form of therapy for post-stroke aphasia.

There are about 15 million strokes worldwide each year. Of this group, about 30% suffer from aphasia. Aphasia is a speech-language disorder associated with exceptional difficulty performing daily communication activities. If no improvement is observed within the first months after the stroke, a complete recovery is unlikely, and the therapy can last for years.

Up to date, speech and language therapy is a standard of care for post-stroke aphasia, however the process is long and demanding.

In the past, several clinical trials aimed to verify the efficacy of language training paired with transcranial direct current stimulation (tDCS), however recent meta-analysis indicates only possible effectiveness (Level C evidence) of anodal tDCS in chronic post-stroke aphasia.

To boost the effects of aphasia rehabilitation, effective brain stimulation protocol still needs to be developed.

Transcranial alternating current stimulation (tACS) can be an interesting alternative to tDCS, as it is able to influence cortical excitability and activity.

Stimulation within high gamma oscillations (60-500Hz) might allow for better speech-language processing, as this band is considered to be the cognitive index of linguistic processes. Moreover, a short period of 75Hz tACS over the motor cortex suggested the positive impact of high-gamma tACS on brain plasticity.

The aim of this RCT is to determine whether 75Hz transcranial alternating current stimulation (tACS) paired with therapeutic linguistic tasks is an effective form of therapy for post-stroke aphasia, measured as an ability to name trained items at 12 weeks follow-up.

Eligibility Criteria:
Individuals with aphasia (assessed using the Boston Diagnostic Aphasia Examination) who perform the Naming Task in the range of 10%-60% accuracy will be included in the study. The overall baseline score in the Naming Task will be estimated from the two baseline measurements.

Inclusion Criteria:

* diagnosis of aphasia: Broca's or mixed (based on the assessment of a Speech Language Pathologist).
* presence of a focus of injury in the left hemisphere (within one hemisphere only) as a result of the first ischemic or hemorrhagic stroke (based on CT/MRI examination);
* chronic stage of the disease - time since the stroke occurred over 6 months.
* ability to achieve an accuracy in the Naming Task of 10-60%.
* 18-80 years
* right-handedness before the stroke.
* ability to give informed written consent.
* fluency in English.

Exclusion Criteria:

* severe cognitive, auditory or visual impairment that would preclude cognitive and language testing - inability to follow a two-step command.
* presence of metal implants in the skull.
* presence of major untreated or unstable psychiatric disease.
* history of epilepsy or seizures.
* ongoing medication that increases the risk of epileptic seizures.
* presence in the body of cardiac stimulators or pacemaker.
* history of speech, language, hearing, or intellectual disability during childhood.
* pregnancy (based on declarations)

Exclusion criteria during the trial:

* high intolerance to stimulation.
* occurrence of an epileptic seizure.
* other previously absent neurological or mental symptoms

Withdrawal criteria:

* high intolerance to stimulation (participants experience severe discomfort during stimulation);
* occurrence of an epileptic seizure;
* other previously absent neurological, physical or mental symptoms.