Effect of Stimulation of the Prefrontal Cortex on Language Production in Aphasic Patients

Effect of Transcranial Direct Current Stimulation of the Prefrontal Cortex on Language Production in Aphasic Patients: a Multicentre Experimental Study With a Placebo-controlled and Double Blind Crossover Design

The purpose of this study is to investigate whether transcranial direct current stimulation (tDCS) of the prefrontal cortex (PFC) influences lexical access and language production. The experimental paradigm will assess the impact of prefrontal stimulation by tDCS versus sham tDCS (S-tDCS) over the PFC of patients with chronic post-stroke aphasia during three language production tasks and a nonverbal executive functions task.

Background: Language processing is a complex brain function supported by a large network, including domain-specific language areas as well as domain-general cognitive-control networks (Friederici & Gierhan, 2013). Noninvasive brain stimulation, such as transcranial direct current stimulation (tDCS), is increasingly being used as a promising therapeutic tool for psychiatric and neurological diseases (Tortella et al., 2015; Flöel, 2014). In the language domain, several studies revealed that tDCS over languagespecific areas induces changes in cortical function that enhances the recovery of language abilities in patients with post-stroke aphasia (Torres, Drebing & Hamilton, 2013; Monti et al., 2013). Beneficial effects of tDCS have also been found for stimulation over more domain-general cognitive control regions. Although research on non-invasive brain stimulation and aphasia reveals promising results, studies investigating the modulation of cognitive control-networks on lexical access are rare. Given the importance of a successful interplay between prefrontal and domain-specific language areas, possible therapeutic effects of tDCS over the prefrontal cortex (PFC) in aphasia can be of high value for rehabilitation and basic research. Procedure: A planned total of 30 patients will be included. In a first visit, the severity of aphasia, the medical history as well as inclusion/exclusion criteria will be evaluated. After this visit, patients will undergo two tDCS sessions (one tDCS and one S-tDCS session) with a one week interval between the sessions. Each session consists of an online (during stimulation) and an offline assessment (within 30 minutes after stimulation). Three language tasks and a nonverbal executive function task will be conducted online as well as offline in each of the two sessions (tDCS and S-tDCS).

In tDCS, the prefrontal cortex is stimulated during 20minutes through a weak constant electric current (1-2 mA) through two electrodes in a non-invasive and painless manner.

S-tDCS refers to a control condition in which the subject will receive a brief current in the beginning in order to induce a similar sensation on the scalp as in tDCS, and then the stimulator remains off for the rest of the stimulation time.

Inclusion Criteria: Chronic aphasia due to ischemic or haemorrhagic stroke (> 6 months post-stroke) French as dominant language Right-handedness Left hemisphere lesion with intact bilateral PFC Exclusion Criteria: Diagnosed dementia or psychiatric comorbidity Epileptic seizure within the last 12 months Metallic head implants Pacemaker Inability to understand procedures or insufficient language production abilities pregnancy strong headache on the days of the tDCS sessions consumption of alcohol and/or unprescribed drugs on the days of the tDCS sessions or on the day before

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