The phenotype-associated effectiveness of transcranial neuromodulation strategies for motor speech centers in the rehabilitation of patients with post-stroke sensorimotor aphasia

BACKGROUND: Speech therapy is considered the cornerstone of rehabilitation for patients with post-stroke aphasia. Its effectiveness increases when combined with non-invasive brain stimulation (NIBS). However, some studies do not support the superiority of combined therapy. Conflicting results may be explained by a lack of awareness about the most effective neuromodulation strategies for different clinical and pathogenetic phenotypes in patients with aphasia.

AIM: This study aimed to evaluate the phenotype-associated effectiveness of speech recovery immediately after a course of routine adjuvant repetitive transcranial magnetic stimulation (rTMS) in patients with post-stroke sensorimotor aphasia.

METHODS: The retrospective observational study included 770 patients, aged 27 to 83 years, with confirmed post-stroke sensorimotor aphasia (52.7% male) and 40 healthy volunteers, aged 30 to 82 years (52.5% male). Speech dysfunction was assessed using the Speech Function Assessment Scale (SFAS), with a score range of 1 to 25. Based on the identified patterns of electroencephalographic interhemispheric cross-correlation in symmetrical leads corresponding to the Broca’s area and its homologue, patients were divided into four phenotypes. Phenotype 1: positive correlation with a positive lag (leading activation of the dominant hemisphere) or zero lag. Phenotype 2: positive correlation with a negative lag (leading activation of the non-dominant hemisphere). Phenotype 3: negative correlation. Phenotype 4: no correlation. Depending on their phenotype, patients received high-frequency rTMS to the affected hemisphere and low-frequency rTMS to the unaffected hemisphere. In the control subgroups, NIBS was not performed. Clinical efficacy was assessed immediately after the end of treatment using the criterion of transitioning to a group with better recovery parameters and specific SFAS scores.

RESULTS: Both rTMS strategies demonstrated better clinical effectiveness in patients with phenotype 3, in phenotype 2 patients in the high-frequency rTMS subgroup, and phenotype 4 patients in the low-frequency rTMS subgroup. Patients with phenotype 1 reported lower clinical effectiveness in the rTMS subgroups than in the control subgroup.

CONCLUSION: The effectiveness of speech recovery after a course of adjuvant rTMS in patients with post-stroke sensorimotor aphasia depends on the alignment of the neuromodulation strategy with the phenotype of the interhemispheric interaction between the Broca’s area and its homologue.