Mapping language area in the frontal lobe of the left-dominant hemisphere with high gamma electrocorticography

Localization of the language-related brain regions is a critical yet challenging issue for neurosurgery. In the present study, investigation of the language-related brain regions were carried out in fourteen patients with a left dominant hemisphere and left frontal or temporal epilepsy using high gamma electrocorticography (ECoG). The patients participated in an ECoG-based language mapping procedure, in which they were required to perform both a word-repeating task and a picture-naming task. Electrodes with significant high gamma (60-140 Hz) responses were regarded as language positive sites. fMRI and electrical cortical stimulation (ECS) with similar language tasks were also performed for comparison. In these fourteen patients, at total of 60, 81, and 105 language positive electrodes were identified with ECS, ECoG, and fMRI, respectively. Using the ECS mapping results as reference, the sensitivity and specificity of the ECoG mapping were 83.2 ± 4.5% and 97.2 ± 0.5%. These results were significantly better than fMRI mapping, which showed a sensitivity of 61.6 ± 6.5% and a specificity of 93.8 ± 0.8%. ECoG mapping was also a better predictor of post-surgery aphasia than fMRI (75% vs. 50%, for a total number of six patients with post-surgery aphasia). If excluding the isolated ECoG positive sites with no neighboring activations, the aphasia prediction accuracy by ECoG can be improved to 100% (six out of six patients). Our results suggest high gamma ECoG mapping as a useful tool for language function protection in epilepsy treatment.