Knowledge Vault 3/14 - G.TEC BCI & Neurotechnology Spring School 2024 - Day 2
Optimizing open-loop and closed-loop brain stimulation procedures
Johannes Gruenwald, g.tec medical engineering GmbH (AT)
<Resume Image >

Concept Graph & Resume using Claude 3 Opus | Chat GPT4 | Llama 3:

graph LR classDef gtec fill:#f9d4d4, font-weight:bold, font-size:14px; classDef stimulation fill:#d4f9d4, font-weight:bold, font-size:14px; classDef experiments fill:#d4d4f9, font-weight:bold, font-size:14px; classDef applications fill:#f9f9d4, font-weight:bold, font-size:14px; classDef discussion fill:#f9d4f9, font-weight:bold, font-size:14px; A[Main] --> B[Grunwald: brain stimulation
research setup. 1] A --> C[Setup: stimulator, amplifier,
switching unit. 2] C --> D[Open-loop: fixed params,
closed-loop: biomarker feedback. 3] C --> E[USB control, faster
hardware triggering. 4] C --> F[G-Hysis Simulink: rapid
prototyping experiments. 5] C --> G[Programmable switching matrix:
16 stim, 256 record. 6] G --> H[Fast switching: 200 Hz,
keep channels connected. 7] C --> I[Impedance check: 1 kOhm
to 1 MOhm, 20 Hz - 1 kHz. 8] I --> J[Spectral, topographic impedance
views pre-stim. 9] C --> K[Interconnect stimulator, switch
unit per use case. 10] A --> L[Clinical apps: brain mapping,
Parkinson's, epilepsy treatment. 11] L --> M[ECS: current injection,
exhibit/inhibit function. 12] M --> N[ECS: 300-500 us, 2-15 mA,
50-60 Hz pulses. 13] M --> O[ECS effects: motor, sensory,
perceptual responses. 14] M --> P[ECS demo: real-time recording,
disconnected stim channels. 15] L --> Q[CCEPs: 5-50 mA, 1 Hz,
maps cortical connectivity. 16] Q --> R[CCEP screening: automated
multi-site stim, record. 17] L --> S[Adaptive DBS: triggered by
high beta in STN. 18] S --> T[Demo: sinusoidal threshold
triggers real-time DBS. 19] A --> U[GTEC Unicorn vs Estim Pro,
PhD experience discussed. 20] U --> V[Estim Pro: wired, no
impedance tomography. 21] U --> W[APIs: low-level access,
proprietary core code. 22] U --> X[Select low impedance
channels for stim. 23] U --> Y[Impedance varies with
frequency, tissue properties. 24] U --> Z[Fast switch 6 ms
post-stim, avoid saturation. 25] Z --> AA[Careful stim current on
recording channel. 26] L --> AB[Adaptive STN DBS reliable
for pre-movement tremor. 27] U --> AC[Exposed 1 mm2 electrodes
possible, manage impedance. 28] A --> AD[More questions, limited time,
suggests Q&A later. 29] A --> AE[Video on YouTube for
later reference. 30] class A,B,U,W,AC,AD,AE gtec; class C,D,E,F,G,H,I,J,K,M,N,O,P,Q,R,S,T,V,X,Y,Z,AA,AB stimulation; class L applications; class Z discussion;


1.-Johannes Grünwald discusses optimizing open-loop and closed-loop brain stimulation procedures using a multipurpose brain stimulation research setup developed at GTEC.

2.-The setup consists of a stimulator (G-Astim Pro), biosignal amplifier (G-HiAmp), and switching unit to route stimulation current to programmed channels.

3.-Open-loop stimulation sets parameters without direct feedback. Closed-loop incorporates biomarker feedback from the amplifier to change stimulation in real-time.

4.-Devices can be controlled by software via USB or faster using hardware trigger cables to react to each other's activation.

5.-The G-Hysis Simulink library containing building blocks allows for rapid prototyping of open-loop and closed-loop neuromodulation experiments.

6.-The switching unit is a programmable switching matrix routing 16 stim channels to 256 electrodes and enabling recording during stimulation.

7.-Fast switching mode allows iterating stimulation channels up to 200 Hz by keeping them connected to the amplifier, with some considerations.

8.-Before an experiment, electrodes are checked for impedance between 1 kOhm to 1 MOhm at 20 Hz to 1 kHz frequencies.

9.-The impedance measurement tool provides spectral and topographical electrode impedance views to identify and document any bad channels before stimulation.

10.-Interconnecting the stimulator and switching unit depends on the desired neurostimulation use case - parallel, triggered, or as master/slave.

11.-Main clinical applications driving research are identifying brain functions via stimulation and treating disorders like Parkinson's and epilepsy.

12.-Electrical cortical stimulation (ECS) injects current to override regional physiology, exhibiting or inhibiting functions to map the eloquent cortex.

13.-ECS uses rectangular pulses of 300-500 µs, 2-15 mA, 50-60 Hz for seconds, starting low and incrementing until behavioral response.

14.-Examples show ECS affecting hand motor control, inducing facial percepts from occipitotemporal stimulation, and chromatic percepts centimeters away.

15.-A Simulink demo selects ECS stimulation channels and displays real-time recording, with disconnected stimulated channels and artifacts on the rest.

16.-Cortico-cortical evoked potentials (CCEPs) from 5-50 mA, 1 Hz stimulation reveals physiological and pathological connectivity between cortical sites.

17.-CCEP screening automatically stimulates and records averaged responses across multiple sites to map connections like Broca's to Wernicke's area.

18.-For Parkinson's, adaptive deep brain stimulation triggered by high beta power in the subthalamic nucleus reduces symptoms better than continuous.

19.-In a demo, extracted sinusoidal amplitudes exceeding a threshold trigger stimulation of configured channel pairs in real-time using the setup.

20.-Differences between the GTEC Unicorn EEG system and Estim Pro stimulator, and the interesting experience of doing a PhD at GTEC are discussed.

21.-The Estim Pro cannot stimulate wirelessly as it requires wired charge transfer. Electrode impedance tomography is not a built-in feature.

22.-MATLAB and C++ APIs enable low-level hardware access, stimulus programming, and GUI analysis, with the core code proprietary to GTEC.

23.-Low impedance stimulation channels should be selected, as high impedance cannot ensure delivered current reaches the brain as desired.

24.-Impedance changes with frequency due to capacitive and resistive properties of tissues that absorb quick alternating charges differently.

25.-Fast switching from stimulation to recording is achieved by the amplifier not saturating, allowing artifact removal 6 ms post-stimulation.

26.-Recording is possible on the stimulating channel using fast mode, with the amplifier connected, but carefully limited stimulation current.

27.-Adaptive DBS based on subthalamic beta power biomarker provides reliable tremor reduction by stimulating in response to the pre-movement increase.

28.-Stimulation is possible with exposed needle electrode areas as small as 1 mm², with impedance and current managed accordingly.

29.-With increasingly more questions and limited time, Johannes suggests using the Q&A for further discussion after the presentation.

30.-The presentation video will be available on YouTube for later reference, as the Spring School is being streamed there.

Knowledge Vault built byDavid Vivancos 2024