Transcranial Direct Current Stimulation to Enhance Training Effectiveness in Chronic Post-Stroke Aphasia

Inclusion Criteria: * left-hemisphere cortical or subcortical stroke with first-ever aphasic symptoms * at least 6 months post-onset of stroke; * aphasia, as determined by the Aachen Aphasia Test (AAT); * 13 moderate-to-severe word finding difficulties (maximum of 75% correct items on a computerized naming task at baseline); * at least 1 correct reaction on the first part of the AAT subscale Token Test (ensuring basic comprehension skills); * at least 1 point on the communicative task of the AAT subscale Spontaneous Speech (ensuring basic communication abilities); * German as first language; * intact left-hemisphere "hand knob" without right prefrontal lesions for placement of tDCS electrodes, as confirmed by magnetic resonance imaging or computer tomography scans. Exclusion Criteria: * contraindications for tDCS (e.g., cardiac pacemaker, history of seizures, implanted metal inside the head); * more than one clinically apparent stroke with aphasic symptoms; * other severe neurological diseases (e.g., brain tumor, and subdural hematoma); * epilepsy with seizures during the last 12 months prior to study start and/or intake of sedating antiepileptic drugs (barbiturates and benzodiazepines), * history of severe alcohol or drug abuse; * current severe depression; * current psychosis or other relevant psychiatric condition; * very severe apraxia of speech, as revealed by Hierarchical Word Lists; * severe non-verbal cognitive deficits, as indicated by the Corsi Block-Tapping Task; * severe uncontrolled medical problems; * severely impaired vision or hearing that prevents patients from engaging in intensive SLT; * changes in centrally active drugs within 2 weeks prior to study inclusion.