Analysis, Design, and Control of

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Analysis, Design, and Control of Movable
Neuro-Probes
Z. Nenadic, E. Branchaud, R.
Andersen, J. Pezaris, W. Collins, and J.
Burdick B. Greger, B. Pesaran
Engineering and Applied Science
Biology California
Institute of Technology
(Auxiliary Program Started April 1, 2001)
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Limitations of Current Neuro-Probe Technology
Key Challenge record high quality signals from
many neurons (for months/years)

• Fixed positioning of implant
• Non-optimal (or wrong!) receptive fields.
• Electrode not near cell body.
• Low impedance (poor SNR) design required.
• Gliosis and encapsulation

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• Movable Probe Concept computer controlled
  movable probes can
• track moving neurons, find new neurons, break
  through encapsulation.
• Project Goals
• Short term validate concept, enable more
  complex acute experiments
• Intermediate term Develop design specs for MEMS
  devices
• Long term develop MEMS technology for
  implantable devices (see talk by Y.C. Tai)

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Current Research Program Outline

• Theory develop algorithms for probe control
  using modeled (computational) environment
• Model extra-cellular neuron potentials
• Characterize local field potentials (LFP)
• Control algorithm development guided by
  computational model

• Implementation meso-scale hardware test-beds
• Validate concept, evaluate algorithms
• Enable testing of Biomechanical issues of
  chronic movable probe operation

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Single Cell Extracellular Potential Simulation
3720 compartment NEURON pyramidal cell model
(adapted from Mainen Sejnowski 96) Synaptic
inputs scattered uniformly throughout dendrites.
Laplace equation Boundary condition Since
solution nearly impossible, use line source
approximation (Holt Koch 99)
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(No Transcript)
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Spatial Variation of Extracellular Potential
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Peak-to-peak amplitude Tuning curve
Added noise -- independent, Gaussian, zero-mean
Noise variance -- determined by signal-to-noise
ratio (SNR)
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Movable Probe Feedback
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Movie 1
Movie 2
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Movable Probe Test-bed Development

• Multiple development phases to maximize
  scientific gain and engineering development along
  the way.
• Acute probes inserted in brain tissue for a
  few hours
• Initial validation of movable probe concept and
  algorithms
• Enable better short-term prosthetic feedback
  experiments
• Semi-chronic electrodes remain, motors
  removed
• Understand biophysical issues of chronic probe
  operation
• Track neural populations over days for plasticity
  studies
• Will set spec.s for future MEMS devices
• Chronic movable system permanently implanted
• Ultimate goal needs MEMS development
• Key technology for future neural-prosthetics

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Acute Test-Beds

• Last time motorizing the CCMD, a pre-existing
  manual 4 probe device
• Completed, with lessons learned
• (need to list some lessons here)

Put diagram of Thomas system here a few words
about status
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Semi-Chronic Test-bed

• Phase I(a) two motor drive that fits inside head
  cap
• Motors and electrodes stay inserted for a few
  days
• Power, control, data wires attached at start of
  each session
• Useful for studies in learning and plasticity
• Phase I(b) two motor drive that fits inside head
  cap
• motors detached at end of every
  sessionelectrodes stay implanted for long
  periods of time.
• enables testing of long term biophysical impact
  of chronic electrode operation (inflammation,
  gliosis, etc.)
• Phase II 12-16 motor micro-drive with removable
  motor assembly. Will enable consistent
  recordings of many cells

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Phase 1 Design Progress
Pretty Picture
Pretty Picture
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Conclusions

• Developed theory for control of movable probe
  based on peak-to-peak amplitude. Future
  investigations will include
• other wave form features, such as phase, shape,
  frequency, etc.
• event detection algorithms to handle
  irregularity of spike trains
• the effects of multiple units (inclusion of
  spike sorting).
• effects of tissue dimpling and relaxation
  (easily incorporated)
• Movable Probe Test-Beds development program
  started
• CCMD motorization completed, with lessons
  learned.
• 5-probe acute system developed
• Phase I of semi-chronic system largely designed