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

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).

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