Language Monitoring in Brain Surgery Under General Anesthesia

Awake surgeries for cerebral lesion resection have several limitations including patient fear, discomfort, or pain. This study aimed to determine whether components of language function could be measured under general anesthesia. In this study, the occurrence of mismatch negativity (MMN) was searched in evoked potentials for phonological sounds.

Five normal hearing, French native speaker, awake volunteers participated in evaluating the phonological task (4 females and 1 male). Eleven normal-hearing, French native speaker patients (6 left and 5 right hemisphere lesions) participated at the time of their tumor neurosurgery (3 females and 8 males). Repetitions of the standard syllable /pa/ with the insertion of 1 deviant /po/ were presented through earphones. The difference between averaged epochs of standards and deviants syllables determined the MMN. During surgery, total intravenous anesthesia was performed with propofol and synthetic opioid sufentanil. The bispectral index was targeted (40 to 60).

The MMN was found in all awake volunteers and validated by an N250 component. In the patient group, the electroencephalogram analysis was not possible in 4 of 11 patients because of anesthesia being too deep, burst suppression, or a high level of noise (>40 μV). Significant N250 response was obtained in 5 of 7 (71.4%) patients under general anesthesia. The 2 other patients also showed MMN which did not reach significance.

To our knowledge, this is the first demonstration that phonological processing can be measured during brain surgery under general anesthesia, suggesting that some language processing persists under the condition of unconsciousness. These results encourage further study of language processing under general anesthesia with the goal of making intraoperative neuromonitoring.