• Florian Le Lann, Justine Cristante, Emmanuel De Schlichting, Romain Quehan, Emilie Réhault, Jean-Albert Lotterie, and Franck-Emmanuel Roux.
• Pole Neurosciences (Neurochirurgie), Centre Hospitalo-Universitaire de Toulouse, Toulouse, France; Université de Toulouse, UPS, Toulouse, France. Electronic address: f.lelann@hotmail.fr.
• World Neurosurg. 2022 Aug 1; 164: e194-e202.

ObjectiveThe authors analyzed the current-intensity thresholds for electrostimulation of language fasciculi and the possible consequences of threshold variability on brain mapping.MethodsA prospective protocol of subcortical electrostimulation was used in 50 patients undergoing brain mapping, directly stimulating presumed language fasciculi identified by diffusion tensor imaging.ResultsThe stimulation-intensity thresholds for identification of language fasciculi varied among patients (mean minimum current intensity of 4.4 mA, range = 1.5-10 mA, standard deviation = 1.1 mA), and 23% of fascicular interferences were detected only above 5 mA. Repeated stimulation of the same site with the same intensity led to different types of interferences in 20% of patients, and a higher current intensity led to changes in the type of response in 27%. The mean minimum stimulation intensities did not differ significantly between different fasciculi, between the different types of interference obtained, or with age, sex, or type of tumor. Positive results on cortical mapping were significantly associated with positive results on subcortical mapping (P < 0.001). Subcortical intensity thresholds were slightly lower than cortical ones (mean = 4.43 vs. 5.25 mA, P = 0.034). In 23 of 50 subcortical mappings, fascicular stimulation produced no language interference.ConclusionsIndividual variability of minimum stimulation-intensity thresholds for identification of language fasciculi is frequent. Nevertheless, even when a high current intensity was used, many stimulations on language fasciculi remained negative for various hypothetic reasons. Finding the optimal current intensity for identifying language fasciculi is of paramount importance to refine the clinical results and scientific data derived from brain mapping.Copyright © 2022 Elsevier Inc. All rights reserved.

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