The End Of Knowledge - Vault 3 - G.TEC BCI & Neurotechnology Spring School 2024 - Day 4

graph LR classDef main fill:#f9d4d4, font-weight:bold, font-size:14px; classDef brain fill:#d4f9d4, font-weight:bold, font-size:14px; classDef signal fill:#d4d4f9, font-weight:bold, font-size:14px; classDef biomarker fill:#f9f9d4, font-weight:bold, font-size:14px; classDef network fill:#f9d4f9, font-weight:bold, font-size:14px; A[Dora Hermes] --> B[combines ecog, stimulation, fMRI
to study brain. 1] B --> C[Electrical stimulation with recordings, DTI
understand networks, health. 2] A --> D[Evoked potentials indicate circuit health,
used clinically. 3] A --> E[Intracranial electrodes stimulate, record responses
across fiber bundles. 4] A --> F[Humans have prolonged myelination,
neural propagation properties measured. 5] F --> G[Arcuate fasciculus conduction speed
measured in 74 patients. 6] G --> H[Conduction delay decreased, speed increased
with age across tracts. 7] H --> I[Speed increased 2 m/s in children
to 6 m/s in adults. 8] H --> J[U-fibers slower than cortical-cortical tracts,
sensory-motor matured faster. 9] F --> K[Propagation timescales change across lifespan,
brain constantly updates. 10] A --> L[HAP waveform potential biomarker
of limbic memory subsystem. 11] L --> M[Less than 50% hippocampus-posterior cingulate
connections had direct N1. 12] L --> N[Stimulation polarity, location traced
indirect HAP pathway. 13] L --> O[HAP waveform proposed novel
limbic memory biomarker. 14] A --> P[Convergent paradigms map inputs,
anatomy in understudied circuits. 15] P --> Q[Basis Profile Curve Identification clusters
sites evoking similar responses. 16] Q --> R[Distinct basis profile curve shapes
in one subject's collateral sulcus. 17] Q --> S[Consensus basis profile curves identified
across subjects in collateral sulcus. 18] P --> T[Hippocampal, amygdalar stimulation suppressed
broadband activity in collateral sulcus. 19] P --> U[Spectro-temporal response clustering suggests
different circuit responses by input. 20] A --> V[CCEPs tested as biomarkers
in 10 epilepsy patients. 21] V --> W[CCEP amplitudes decreased after
thalamic stimulation. 22] A --> X[Neural transmission speeds increase
2-fold childhood to adulthood. 23] A --> Y[HAP waveform propagates through
limbic memory subsystem. 24] A --> Z[Stimulation-evoked response shapes vary
with anatomical input type. 25] A --> AA[Spectro-temporal profiles of CCEPs
differ by input type. 26] A --> AB[Stimulation-evoked potentials promising
brain circuit biomarkers. 27] A --> AC[Data and code from studies
openly shared for reproducibility. 28] A --> AD[Stimulation currents under 6mA,
200us pulses used. 29] A --> AE[Future work: stimulation mimicking normal activity,
CCEP features and cognitive processes. 30] class A main; class B,C,E,F,G,H,I,J,K brain; class D,L,M,N,O,V,W,X,Y,AA,AB,AC biomarker; class P,Q,R,S,T,U,Z network; class AD,AE signal;

Resume:

1.- Dora Hermes, a biomedical engineering professor at Mayo Clinic, combines ecog, brain stimulation, and fMRI to study human brain networks.

2.- Electrical brain stimulation combined with intracranial recordings and DTI imaging helps understand human brain networks and circuit health.

3.- Evoked potentials from stimulation, used as biomarkers, indicate circuit health. Brainstem auditory evoked potentials are used clinically.

4.- Intracranial electrodes allow stimulating and recording responses across fiber bundles to assess typical signal propagation and identify atypical responses.

5.- Humans have prolonged myelination compared to other species, so neural signal propagation properties must be measured in the human brain.

6.- The arcuate fasciculus conduction speed was measured in 74 patients to understand typical transmission with age.

7.- Conduction delay decreased and speed increased significantly with age across major association tracts like arcuate fasciculus and superior longitudinal fasciculus.

8.- Conduction speed increased from 2 m/s in children to 6 m/s in adults for long association tracts.

9.- U-fibers had slower conduction speeds compared to long cortical-cortical tracts. Sensory-motor connections matured faster than frontal-parietal connections.

10.- Timescales of neural signal propagation change across the lifespan and the brain must constantly update itself. Data is shared openly.

11.- The hippocampus-anterior cingulate-posterior cingulate (HAP) waveform is a potential biomarker of the limbic memory subsystem.

12.- Less than 50% of hippocampus-posterior cingulate connections had a direct N1 response, suggesting indirect connectivity best identified by canonical parameterization.

13.- Stimulation polarity and location helped trace the indirect HAP pathway from anterior to posterior hippocampus to anterior thalamus to posterior cingulate.

14.- The HAP waveform is proposed as a novel electrophysiological biomarker of limbic memory subsystem connectivity.

15.- Convergent paradigms, measuring responses at one site from stimulation at many, can map inputs and anatomy in understudied circuits.

16.- Basis Profile Curve Identification clusters stimulation sites evoking similar response shapes to map anatomical inputs to a region.

17.- In an example, sites in hippocampus, amygdala, and insula evoked distinct basis profile curve shapes in one subject's collateral sulcus.

18.- Consensus basis profile curves, representing canonical anatomical input clusters, were identified across subjects in the collateral sulcus.

19.- Hippocampal and amygdalar stimulation suppressed broadband activity in the collateral sulcus, while other sites had less effect.

20.- Spectro-temporal response clustering suggests different circuit responses based on anatomical input type, possibly reflecting feedforward, feedback, and lateral influences.

21.- CCEPs as biomarkers were tested in 10 epilepsy patients to assess effects of anterior thalamic DBS on network excitability.

22.- CCEP amplitudes decreased after thalamic stimulation, demonstrating CCEPs can track stimulation-induced network changes as potential treatment biomarkers.

23.- In summary, neural signal transmission speeds increase over 2-fold from childhood to adulthood, matching neuroimaging findings of prolonged development.

24.- The HAP waveform propagates through the limbic memory subsystem and is a potential circuit biomarker.

25.- Stimulation-evoked response shapes vary with anatomical input type and can be clustered to map connections in understudied networks.

26.- Spectro-temporal profiles of CCEPs also differ by input type, providing additional information about the nature of the connection.

27.- Overall, stimulation-evoked potentials are promising brain circuit biomarkers to study development, myelination, signal propagation, and effects of interventions.

28.- Data and code from published studies are openly shared to enable reproducibility.

29.- Stimulation currents under 6mA with 200µs pulses are used, with precautions to avoid inducing seizures. Effects on local cells are unclear.

30.- Future work could investigate stimulation parameters mimicking normal activity, and how CCEP features relate to normal cognitive process and abnormal epileptiform activity.

Knowledge Vault built byDavid Vivancos 2024