16Channel Brain Tissue Stimulator

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16-Channel Brain Tissue Stimulator
Friday, October 27, 2006
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Design Team

• Team Members
• Ashley Phillips -Team Leader
• Nina Lewis - Communications
• Steven Skroch - BSAC
• Steve Noel - BWIG
• Client
• Matthew Jones, PhD Department of Physiology
• Advisor
• Willis Tompkins, PhD Department of Biomedical
  Engineering

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Overview

• Problem Statement
• Motivation
• Background
• Design
• Future Work

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Problem Statement

• Our objective is to develop a multi-channel brain
  tissue stimulator. This device must generate
  stimulation current of 1 mA on 16 separate
  channels, filter out external noise, and allow
  each channel to be independently gated on and off
  as well as adjust the current amplitude on each
  channel.

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Motivation

• To learn the circuitry of the hippocampus to
  better understand the processes behind learning
  and memory
• To improve upon the current process, as it is not
  physiologically accurate
• Provide a low cost multi-channel stimulator

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Background

• Hippocampus
• Site for learning and memory
• Receives inhibitory and excitatory potentials
  from neurons in the cortex
• Contains tightly packed granule cells, called
  dentate gyrus, which form one unit of circuitry

(1)
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Background

• Michigan Electrode
• 16 electrodes
• Each channel of device will stimulate one
  electrode
• Each electrode has high impedance of 1 MO
• AC current only

(2)
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Client Requirements

• The stimulator should
• Trigger each pad independently with a 5V TTL
  pulse
• Deliver 1 mA of current
• Deliver the same amount of current to each pad
• Deliver the pulse in 100?s with no lag

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Problems Encountered

• Lag time cannot be completely eliminated
• High voltage must be supplied
• Safety

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Proposed Design
(3), (4), 5), (6)
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Rectifier
12
Switch
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Future Work

• Order parts
• Build and test circuit
• Scale-up circuit
• Build at least 2 channels

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References/Acknowledgments

• www.BrainConnection.com
• Jones, Matthew. Personal interview. 15 Sept.
  2006.
• Kaczmarek, Kurt A., Kevin M. Kramer, John G.
  Webster, and Robert G. Radwin. "A 16-Channel
  8-Parameter Waveform Electrotactile Stimulation
  System." IEEE Transactions on Biomedical
  Engineering 38 (1991) 933-943.
• Yusko, Erik, Danielle Ebben, Marty Grasse, and
  Tony Wampole. 16-Channel Brain Tissue Stimulator.
  UW-Madison. 1-26.
• Victorey, Paul. Department of Biomedical
  Engineering. Personal Interviews.
• ONeal, Burke L. Department of Biomedical
  Engineering. Personal Interviews.

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Any Questions?
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Modifications to Original Design

• Replaced 50kO ½ W Filter resistors with 5MO 2.5 W
  Resistors
• 470 µF capacitors only rated to 300 V. Will
  have to replace when we scale up
• 22 µF capacitor for charge storage (may
  eliminate)
• All components must be high power

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Switch

• 5V pulse sent through Schmitt Trigger for
  normalization
• Pulse sent through optical isolator
• Want to keep entire gate side of circuit floating
• 12V Floating Source, rated to 700 V
• FET rated up to 1000Vds

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Switch

• Potentiometer used to modify output voltage (may
  move to before gate)
• Only the FET must be high power
• All components must have minimal attenuation at
  100kHz
• No leakage current due to probe acting as a
  capacitor (cannot pass DC current)