Knowledge Vault 3/94 - G.TEC BCI & Neurotechnology Spring School 2024 - Day 10
High-gamma activity mapping in the neurosurgical field
Takahiro Sanada, Asahikawa Medical Universit (JP)
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Concept Graph & Resume using Claude 3 Opus | Chat GPT4 | Llama 3:

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1.- Dr. Takahiro Sanada is a neurosurgeon at Asahikawa Medical University in Hokkaido, Japan, located 5 hours from Sapporo by train.

2.- Dr. Sanada discusses high gamma activity mapping in neurosurgery, using examples from his own research and clinical work.

3.- Electrocortical stimulation (ECS) mapping is a classic but subjective method to identify functional brain areas during awake brain surgery.

4.- ECS was used to map language areas in a patient with a left temporal brain tumor prior to resection.

5.- High gamma activity mapping using ECoG is an objective, quantitative alternative to ECS that doesn't require direct brain stimulation.

6.- Dr. Sanada's group uses G.Tec equipment to measure ECoG and analyze high gamma activity in real-time during brain mapping.

7.- Advanced intraoperative high gamma mapping can identify language areas like Wernicke's and Broca's areas without needing patient cooperation.

8.- "Asleep-awake-asleep" brain mapping was done using high gamma ECoG to preserve language function while maximally resecting a tumor.

9.- Repeated hand grasping tasks cause attenuation of high gamma activity over time in sensorimotor cortex, based on previous studies.

10.- Dr. Sanada's study tested high gamma attenuation in sensorimotor cortex during repeated grasping in 11 patients using subdural ECoG.

11.- 3D brain models were made by co-registering post-op MRI and CT to localize ECoG electrodes on the brain surface.

12.- Patients did 10 rounds of 10 hand grasping movements each while high gamma activity was recorded from sensorimotor electrodes.

13.- High gamma activity was compared between grasps and between rounds to quantify short-term and long-term attenuation.

14.- High gamma activity attenuated significantly from the 1st to 2nd and 2nd to 3rd grasps within rounds.

15.- High gamma activity also attenuated after the 1st round compared to later rounds, localizing most to the hand area.

16.- Single-trial analysis found high gamma peaked 700ms after movement onset and was higher for the 1st vs. 9th grasp.

17.- More sensorimotor electrodes showed long-term (50%) vs. short-term (25%) high gamma attenuation, especially near the anatomical hand knob.

18.- High gamma attenuation reduces the signal available for brain mapping, so paradigms should minimize grasps per round to maximize power.

19.- Prosopagnosia is impaired face recognition despite intact vision, associated with damage to the fusiform gyrus and inferior temporal gyrus.

20.- fMRI, ECoG, and ECS were compared for mapping face recognition areas in 5 epilepsy patients with implanted subdural electrodes.

21.- fMRI and ECoG detected more face-specific responses than ECS alone, but fMRI was affected by artifacts from skull base air spaces.

22.- ECoG had few artifacts and better detection than ECS, which only locally stimulated parts of the distributed face network.

23.- Combined fMRI and ECoG identified putative face areas ECS could not find that were safely resected without causing prosopagnosia.

24.- The CORTEQ 3D brain montage creator is a useful tool for making 3D electrode models for ECoG analysis.

25.- 3D brain montages can be made using pre-op MRI plus post-op CT, or using intra-op pictures when post-op CT is unavailable.

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