Artikel
Observer-independent language mapping using a semantic decision task
Untersucher-unabhängige Sprachkartierung mittels einer semantischen Entscheidungsaufgabe
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Autoren
Veröffentlicht: | 8. Mai 2019 |
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Gliederung
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Objective: Picture naming is the most widely used task for language mapping in the context of neurological surgery but requires a high level of expertise from the investigator and is highly observer-dependent. Moreover, online-analysis of language errors is challenging, whereas offline video-analysis is very time-consuming and not applicable for intraoperative monitoring. We, thus, set out to (1) investigate an observer-independent semantic decision task via functional magnetic resonance imaging (fMRI) and (2) implement this task for the use by navigated transcranial magnetic stimulation (nTMS) and intraoperative direct cortical stimulation (DCS).
Methods: The semantic decision task consisted of an auditive presentation of complex sentences. After this, subjects were asked to choose the drawing of a semantically related object via button press (one out of three). The control conditions consisted of nonsense sentences and reverse speech. After this, subjects were asked to choose (out of three) the drawing of a semantically related object via button press. Reaction times and responses were registered. First, the task was tested in n=20 healthy, right-handed subjects using sparse-sampling fMRI (3T) which allows to avoid contamination of the activation by acoustic scanner noise. Then, the task was integrated into the nTMS setting and made available for task-locked intraoperative DCS.
Results: The fMRI experiment showed excellent feasibility of the task and demonstrated specific activations in the language network, particularly within the inferior frontal gyrus and the posterior middle temporal gyrus, as well as a left-lateralization. The task-design allowed to measure the reaction times and correctness of picture choice automatically, both being highly stable on the within-subject level. Clinical pilot results from patients including comparison with nTMS and DCS will be presented.
Conclusion: Using a semantic decision task with automatic online-detection of both reaction times and correctness of semantic choice might represent a highly robust and sensitive adjunct to the standard language mapping setting, both intraoperatively and for non-invasive functional diagnostics. However, the method still needs to be validated in a larger subset of patients.