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

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

Overview Problem Statement Motivation Background Design Future Work

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.

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

Background Hippocampus o Site for learning and memory o Receives inhibitory and excitatory potentials from neurons in the cortex o Contains tightly packed granule cells, called dentate gyrus, which form one unit of circuitry (1)

Background Michigan Electrode o 16 electrodes o Each channel of device will stimulate one electrode o Each electrode has high impedance of 1 MΩ o AC current only (2)

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

Problems Encountered Lag time cannot be completely eliminated High voltage must be supplied Safety

Proposed Design (3), (4), 5), (6)

Rectifier

Switch

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

References/Acknowledgments 1) 2) Jones, Matthew. Personal interview. 15 Sept ) 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): ) Yusko, Erik, Danielle Ebben, Marty Grasse, and Tony Wampole. 16-Channel Brain Tissue Stimulator. UW-Madison ) Victorey, Paul. Department of Biomedical Engineering. Personal Interviews. 6) O’Neal, Burke L. Department of Biomedical Engineering. Personal Interviews.

Any Questions?

Modifications to Original Design Replaced 50kΩ ½ W Filter resistors with 5MΩ 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

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

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)