Knowledge Vault 3/100 - G.TEC BCI & Neurotechnology Spring School 2024 - Day 10
High-gamma mapping and gamma echo
Peter Brunner, Washington University School of Medicine (USA)
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Concept Graph & Resume using Claude 3 Opus | Chat GPT4 | Llama 3:

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hardware for BCI. 1-2] A --> C[Invasive BCI: seizure monitoring,
HFO biomarkers. 3] A --> D[ECoG placement in surgery
for high gamma mapping. 4] A --> E[Neuromodulation: brain stimulation
based on activity. 5] A --> F[Pfurtscheller: ERD during
motor imagery. 6] A --> G[Implants need precise
electrode placement. 7] G --> H[High gamma diminishes
with repetitive movements. 9] A --> I[Early ECoG BCIs:
cursor control, DOOM. 11] I --> J[High gamma overshoot
with novel movements. 12] A --> K[ECoG gesture classification
experiments in Japan. 13-14] A --> L[Schalk & Brunner: rapid
cortical mapping system. 16] L --> M[Temporal dynamics of high
gamma during gestures. 17] L --> N[High gamma mapping vs
electrical stimulation. 18-20] N --> O[High gamma: better
resolution, less risk. 20] L --> P[Validation: high gamma vs
fMRI, ECS, micro-ECoG. 23-26] L --> Q[Temporal dynamics of
picture naming. 24] L --> R[Worldwide use of
Cortec-U system. 26] A --> S[CCEPs map networks by
stimulation and recording. 27] A --> T[High-res ECoG: precise
somatotopic finger mapping. 28] A --> U[SSEPs identify central sulcus. 29] A --> V[ECoG BCIs control
prosthetic hands. 30] A --> W[Future: intraoperative studies,
stimulation & passive mapping. 29] class A,B,C,D ecog; class E,F,S,T,U stimulation; class G,H,I,J,K,L,M,N,O,P,Q,R mapping; class V,W future;


1.- Peter Brunner discusses characterizing and modifying cortical processes to map brain function, mainly to guide surgical resections in epilepsy patients.

2.- Two fundamental approaches are electrocorticography (ECoG) with electrode sheets on brain surface and stereo EEG with depth electrodes, which is gaining popularity.

3.- The research is highly interdisciplinary, involving neurosurgery, neuroimaging, experiment design, signal processing, computational neuroscience and broader neuroscience perspectives.

4.- It provides a unique opportunity to work with patients and immediately see outcomes, both in the operating room and at the bedside.

5.- Electrical brain stimulation is used clinically to map critical functions like motor, speech and visual areas prior to epilepsy surgeries.

6.- However, electrical stimulation mapping has limitations - it requires extensive testing, can be non-specific, and risks triggering afterdischarges and seizures.

7.- As an alternative, passive ECoG mapping utilizes low and high frequency oscillations, especially high gamma activity, as indicators of cortical activation.

8.- The clinical vision was a real-time ECoG mapping system that cues subjects to perform actions, records and analyzes signals, and guides surgeons.

9.- Developing the system required electrode localization, software for real-time experiments and analysis, and visualization fusing function with underlying brain anatomy.

10.- Examples demonstrate rapid mapping of hand, tongue, lip, and auditory cortex activation in just 1-2 minutes of ECoG recording.

11.- Extensive engineering was needed to decompose signals into frequency components, extract high gamma activity, and detect cortical activation onset.

12.- Results from adults and children show strong concordance between ECoG high gamma mapping and electrical stimulation, with some greater sensitivity.

13.- Broca's expressive speech area could be mapped with ECoG under anesthesia by analyzing initial cortical responses to receptive language stimuli.

14.- ECoG mapping has been validated across scales from macro to micro grids and shows consistency with fMRI language mapping.

15.- Transitioning ECoG mapping to clinical use required securing IP, designing clinical trials, engineering a device, and navigating FDA approval.

16.- Stimulation artifacts during recordings pose challenges and require special processing to remove without filtering out relevant neural signals.

17.- Novel approaches track gamma activation onsets across trials despite timing variability to reveal underlying oscillatory coupling and information flow.

18.- By titrating acoustic stimuli to perceptual thresholds, ECoG can reveal neural activity governing variable perceptual decisions.

19.- Temporally precise ECoG responses to different categories of acoustic stimuli (speech, music, environmental sounds) reveal distinct spatiotemporal activation patterns.

20.- ECoG also captures predictive responses to expected but omitted stimuli in a regular sequence, activating specific cortical regions.

21.- Electrical stimulation itself can be used to probe functional connectivity by inducing gamma activity and observing its propagation.

22.- Applying spatial and temporal filtering to remove stimulation artifacts allows tracking the spread of induced gamma oscillations.

23.- The early and late components of the cortical stimulation response, the CCEP and gamma echo, reveal different connectivity profiles.

24.- Convergence between ECoG responses to acoustic stimuli and cortical stimulation further supports the mapping of functional language networks.

25.- Single pulse electrical stimulation delivered through depth electrodes and recorded with scalp EEG helps localize subcortical DBS targets.

26.- Stimulation evoked potentials also guide positioning within small subcortical nuclei like the GPi for movement disorders.

27.- SEEG with depth electrodes is increasingly used over ECoG grids as it causes less morbidity while mapping wider brain networks.

28.- However, ECoG has limitations in spatial resolution, coverage of sulci and deeper layers compared to the columnar and laminar organization of cortex.

29.- Future directions include more outcome-based intraoperative and chronic studies and further integration of stimulation with passive ECoG mapping.

30.- In conclusion, ECoG mapping provides concordant results to electrical stimulation and can be used intraoperatively with and without patient participation.

Knowledge Vault built byDavid Vivancos 2024