gms | German Medical Science

Objective: The developmental process of language dominance in children is the subject of current research with hints that this process may vary widely across individuals. Repetitive transcranial magnetic stimulation (rTMS) was used to examine language-involved cortical regions in adults. On the basis of the rTMS error rate, a ratio can be calculated for the assessment of language lateralization. However, little is known about the use of rTMS to study plasticity of language function in children with language-associated lesion.

Methods: In this feasibility study, a consecutive prospectively collected cohort of 12 children with language-associated lesion underwent bihemispheric rTMS mapping prior to surgery (with 100 stimulation sites on each hemisphere). The evaluation of the speech mapping was performed by 2 experienced investigators with many years of rTMS experience in a consensus-based manner. Feasibility and side effects were documented as well as the error rate and error category of each hemisphere. The rTMS-induced speech errors were assigned to the following categories: hesitation, performance, no response, phonological and semantic error.

Results: Repetitive TMS speech mapping was feasible in all 12 patients (median age: 12; range: 4-17) without any severe side effects. Eight patients (67%) had a tumor and 4 patients (33%) suffered from cortical dysplasia or perinatal stroke / hemorrhage. We observed rTMS-induced errors in both hemispheres in all children, with more errors in the left hemisphere (LH) (mean 7.8) compared with the right hemisphere (RH) (mean 4.6) (p = .005). The three children with more / equal errors in the RH were older (median age: 17 years) than the 9 children with more erros in the LH (median age: 12.5 years; p = .092). The most common error category was hesitation error (LH: 39%, RH: 43%). Interestingly, the frequency of no-response errors was nearly twice as high in the LH (22%) as in the right hemisphere (12%) (p = .001).

Conclusion: Bihemispheric rTMS speech mapping in children is feasible with significant more errors being observed on the left hemisphere. Plasticity of language function to the right hemisphere seems to develop rather in older children. Age- and localization-related analyses based on an increased number of patients is our aim to further address lesion induced plasticity of language function in children.