Continuous behavioral tracing-based online functional brain mapping with intracranial electroencephalography

Functional mapping of language-related areas from natural, narrative speech during awake craniotomy surgery

Accurate localization of brain regions responsible for language and cognitive functions in epilepsy patients is important. Electrocorticography (ECoG)-based real-time functional mapping (RTFM) has been shown to be a safer alternative to electrical cortical stimulation mapping (ESM), which is currently the clinical/gold standard. Conventional methods for analyzing RTFM data mostly account for the ECoG signal in certain frequency bands, especially high gamma. Compared to ESM, they have limited accuracy when assessing channel responses. In the present study, we developed a novel RTFM method based on tensor component analysis (TCA) to address the limitations of current estimation methods. Our approach analyzes the whole frequency spectrum of the ECoG signal during natural continuous speech. We construct third-order tensors that contain multichannel time-frequency information and use TCA to extract low-dimensional temporal, spectral and spatial modes. Temporal modulation scores (correlation values) are then calculated between the time series of voice envelope features and TCA-estimated temporal courses, and significant temporal modulation determines which components' channel weightings are displayed to the neurosurgeon as a guide for follow-up ESM. In our experiments, data from thirteen patients with refractory epilepsy were recorded during preoperative evaluation for their epileptogenic zones (EZs), which were located adjacent to the eloquent cortex. Our results showed higher detection accuracy of our proposed method in a narrative speech task, suggesting that our method complements ESM and is an improvement over the prior RTFM method. To our knowledge, this is the first TCA-based method to pinpoint language-specific brain regions during continuous speech that uses whole-band ECoG.

Clinical application of intraoperative trial-free online-based language mapping for patients with refractory epilepsy

OBJECTIVE

The objective of the study was to develop and clinically test a trial-free online-based language mapping method for localizing the eloquent cortex easily in epilepsy operation.

METHODS

Nine patients with refractory epilepsy were included in this study according to the results of preoperative evaluation for their epileptogenic zones (EZs) located adjacent to the eloquent cortex. When patients were awakened up from general anesthesia during operation, the trial-free online-based language-mapping paradigm was performed. All positive points marked on the cortex in each test were labeled and superimposed together as the result of functional mapping for each patient. The eloquent cortex was mapped according to the results obtained both from the intraoperative trial-free task localization method and the traditional electrical cortical stimulation (ECS).

RESULTS

All patients completed this paradigms twice within 10 min. Based on the results of mapping, the EZs were tried to fully resected on the premise of preserving the mapped eloquent cortex as much as possible. The postoperative follow-up showed the outcome of Engel I in six patients and Engel II in three patients, whereas only two patients had aphemia after surgery and recovered within one week and three months, respectively.

SIGNIFICANCE

The intraoperative trial-free online-based language mapping method was primarily identified to be safe and effective. This novel method seems to be promising and worthy of improvement.