Life Sciences Division

Modulation of language functions by transcranial magnetic stimulation

A research team at the Frederic Joliot Hospital Service (CEA Orsay) has succeeded in modulating language performance by targeted transcranial magnetic stimulation. The specific stimulation of the brain areas involved in the functions of language perception significantly lowered response time in a language-processing task. This lowering was more marked when the language was the respondent's mother tongue (French) than when it was a foreign language. These results open interesting perspectives for the therapeutic treatment of certain disorders affecting these functions, in particular medication-resistant schizophrenic hallucinations.

Transcranial magnetic stimulation (TMS) is a non-invasive experimental method that can temporarily modulate brain activity in the stimulated regions. This method was used to modulate language performance in a language-processing task in healthy subjects.

The task consisted in indicating, by pressing one of two response buttons, whether or not a short spoken phrase was part of a preceding utterance.  During the task the subjects were subjected to stimulation specifically localised in the language regions. The response times and error frequencies were measured under active stimulation and placebo in a random order.

Magnetic resonance imaging (MRI) was used to localise areas specifically involved in language processing. The association of functional MRI (fMRI) with auditory stimuli (utterances in French and in foreign languages) was used to localise the regions involved in language perception in each subject (see Figure A).

The upper left temporal area (Wernicke's area) is involved in comprehension, and the frontal opercular area (Broca's area) in speech recognition and production.
A neuronavigation system was then used to guide the low frequency magnetic stimulation (1Hz) individually and in real time towards language areas detected by anatomic and functional MRI (Figure B).

The results showed a significant decrease in response time during active stimulation of Wernicke's area compared with placebo, which was more marked when the phrases were in French rather than in a foreign language.

In contrast, no effect was observed on Broca's area. These findings show that it is possible to modulate language performance through stimulation of a region of the brain supporting language perception functions, and opens perspectives for therapeutic research into certain disorders of these functions, in particular medication-resistant schizophrenic hallucinations (Figure C).

Figure C : Significant shortening of response time under active stimulation compared with placebo stimulation for Wernicke's area. More marked shortening for phrases in French than for those in foreign languages.
NS: non-significant.