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Interfaces to neural systems

Interfaces to neural systems. Chapters 1 and 2 of Neural Engineering, Bin He. Recap on the paper. ASIA – American Spinal Injury Association Level of injury determines how much function is lost (low injury, fewer lost functions). Block diagram should be straightforward.

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Interfaces to neural systems

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  1. Interfaces to neural systems Chapters 1 and 2 of Neural Engineering, Bin He

  2. Recap on the paper • ASIA – American Spinal Injury Association • Level of injury determines how much function is lost (low injury, fewer lost functions). • Block diagram should be straightforward. J Physiology, 2007, Donoghue et al.

  3. Human Brain Jill Bolte Taylor (neuronanatomist who had a hemorrage) shows a human brain

  4. Action potentials

  5. Schwann cells and the myelin sheath

  6. Galvani’s first experiment

  7. The second experiment Can you guess what is going on?

  8. White board break

  9. Interfaces with the nervous system • Majority: electrical • Other ways: chemical (ISE)

  10. High pass electrodes • Electrodes are either polarizable (capacitor-like) or non-polarizable (resistor-like). • Usual metal electrodes: polarizable (high pass)

  11. Needle electrodes • Also known as depth electrodes • Used for cortex when micromachined • Problem: can’t access several layers

  12. Slanted array (Utah) W Rutten, Ann Rev Biomed Eng 2002

  13. Verifying placement and tissue damage after chronic implants • Histological methods • Inflammatory measures • Electrochemical performance

  14. Challenges • How to measure damage without damaging the tissue even more • How to miniaturize the electrode without losing signal

  15. Low pass (or non-polarizableelectrodes): traditional example: Ag/AgCl

  16. Challenges • Ag/AgCl is toxic. • Most electrodes are not only high pass (neither only low pass). • Interfaces are nonlinear • Biocompatibility issues • Miniaturization (“nano-rization”?) brings other parameters to the interface

  17. Ion-selective electrodes • Membrane between sensor and tissue “pre-filters” (selects) ions. • Voltage difference between two electrodes will be proportional to the ratio of the activity inside (ai) and outside (ao). • Electrochemical methods assume the reduction and oxidation of the species on the surface of the electrode

  18. A neuron on a transistor Fromherz & al, Science, 1991.

  19. Si-cell junction • Cell is from a leech. • Gate was not fully oxidised

  20. Do the signals look similar? • ME=microelectrode • FET=transistor

  21. Horizontal needle • Potential fix for depth problem • Active probes • Wireless implants • CMOS-compatible processing

  22. Sieve array

  23. Chemical monitoring microdialysis probes

  24. Detecting seizures • Spectral components. • In slices: works perfectly. In vivo: long shot.

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