Motor or non-motor speech interference? A multimodal fMRI and direct cortical stimulation mapping study

Area of Science:

• Neurosurgery
• Cognitive Neuroscience
• Neurolinguistics

Background:

• Awake surgery for left fronto-temporal low-grade gliomas requires precise mapping of critical brain areas to preserve function.
• Understanding the specific roles of the precentral gyrus and inferior frontal gyrus in speech production is crucial for surgical planning.
• Direct electrical stimulation (DES) combined with functional magnetic resonance imaging (fMRI) offers a powerful tool for intraoperative brain mapping.

Purpose of the Study:

• To investigate the precise localization of speech articulation centers within the left inferior frontal gyrus and precentral cortex using DES.
• To differentiate the neural substrates underlying different types of speech disturbances (motor speech arrest, dysarthria) during awake surgery.
• To correlate intraoperative DES findings with pre-operative fMRI maps for enhanced surgical navigation and functional preservation.

Main Methods:

• Retrospective analysis of 15 patients undergoing awake surgery for left fronto-temporal low-grade gliomas with normal pre-operative cognition.
• Integration of pre-surgical fMRI maps (motor and language centers) with intra-operative DES data (MNI-registered cortical sites).
• Performance of number counting and picture naming tasks during DES to elicit speech disturbances, with analysis of shared voxels between fMRI and DES-identified volumes of interest (VOIs).

Main Results:

• DES of the precentral gyrus evoked motor speech arrest (anarthria), with maximal overlap between fMRI maps of lip/tongue movements and the stimulation site.
• DES of the inferior frontal gyrus (pars opercularis, rolandic operculum) induced speech arrest proper, maximally overlapping with the overt counting fMRI map.
• DES of the inferior frontal gyrus (pars opercularis and triangularis) resulted in dysarthria, with maximal overlap with the silent object naming fMRI map; reduced Broca's area activity was noted during silent vs. overt speech.

Conclusions:

• Direct electrical stimulation effectively differentiates specific speech articulation networks within the left inferior frontal gyrus and precentral cortex.
• The study demonstrates distinct functional roles for different subregions within these areas, correlating with specific speech disturbances.
• Combining fMRI and intraoperative DES provides a robust method for mapping speech functions, enabling safer and more effective surgical interventions for brain tumors.