16-Channel Brain Tissue Stimulator Friday, February 24

Design Team Team Members Marty Grasse – Team Leader Erik Yusko – Communications Tony Wampole – BWIG Danielle Ebben – BSAC Client Dr. Matthew Jones, Dept. of Physiology Advisor Professor Willis Tompkins

Overview Problem Statement Background Client Requirements Design Alternatives 1) Power and signal isolation 2) Amplitude of current waveform control 3) Method of current waveform generation Conclusion Future Work

Problem Statement In order to stimulate neurons in a more realistic manner, an electrical device is needed to independently control current through each electrode in a 16-electrode array. The device must use parallel logic from a computer to control the current. The device must be isolated from electrical noise so the measurements are accurate.

Background Brain functions via network of electrical circuitry (neurons) Excite brain tissue by applying electrical impulses Observing the tissues response to impulses is imperative to understanding of brain physiology as well as brain disorders

Background (Dr. Jones’ work) In vitro stimulation of rodent brain tissue Specifically interested in timing and connectivity of signal transfer within a neural circuit Currently using a large single electrode to stimulate tissue Needs multiple small electrodes to deliver varying magnitudes of current to precise locations in tissue

Block Diagram Power Isolation and voltage step up Voltage to Current Converter Electrode Array

Client Specifications Supply a current stimulus using parallel logic from computer to gate Isolated from AC noise (60 Hz) Independent gain adjustment for each channel Range: 0 mA to 1 mA Electrode impedances up to 3 MOhms Square pulse 25 to 200 usec Very fast rise/fall time Rack-mount chassis

Power Isolation and Supply 60 Hz AC noise Methods of Isolation Battery DC/DC Converters Reference [11]

Power Isolation and Supply Large voltage necessary to guarantee current across electrodes DC/DC converters in series Vs Output voltage is significantly larger than source voltage

Current Control: VIC Transconductance amplifier: V to I Δ Vo receive a corresponding current value. IL = Vo*g m where g m is transconductance of the VIC Reference: [2] Load

Current Control Continued Advantages: Less Expensive Control the sensitivity of the circuit Disadvantages: Not commercially designed and assembled Independent voltage source required for V1

Pulse Control: Potentiometer On/Off control provided by TTL output from PC TTL gates transistor Q1 on/off Vo is controlled by pot, R9. Q1

Pulse Control: Digital TTL Analog Stream: -use an A/D converter -digitally set current output Advantages: - Flexibility - Resolution - Accuracy Disadvantages: - Limited Digital resolution - Workaround: requires microcontroller and timing circuitry

Conclusion Power isolation over Battery supply DC/DC converters Potentiometers to vary voltage input Voltage to current conversion Self-construction Two in One Analog Devices 1B23

Future Work Test sample voltage to current converters Decide on final design Construct and test final design

References 1) Brasil, R.O. Leal-Cardoso, J.H. An optically coupled power stimulus isolation unit with high voltage and fast rise time output. Brazilian Journal of Medical and Biological Research P ) Kaczmarek, Kurt A. Kramer, Kevin M. Webster, John G. Radwin, Robert G. A 16- Channel 8-Parameter Waveform Electrotactile Stimulation System. IEEE Transactions on Biomedical Engineering. Vol. 38, 10. October ) Wu, Han-Chang. Young, Shuenn-Tsong. Kuo, Te-Son. A Versatile Multichannel Direc-Synthesized Electrical Stimulator for FES Applications. IEEE Transactions on Instrumentation and Measurement. Vol. 51, 1. February ) Land, Bruce R. Johnson, Bruce R. Wyttenbach, Robert S. Hoy, Ronald R. Tools for Physiology Labs: Inexpensive Equipment for Physiological Stiumulation. The Journal of Undergraduate Neuroscience Education. June, Fall ) Poletto, Christopher J. Van Doren, Clayton L. A High Voltage, Constant Current Stimulator for Electrocutaneous Stimulation Through Small Electrodes. IEEE Transactions on Biomedical Engineering. Vol. 46, 8. August ) Wikipedia. Current Source. Recovered [Online] 7) Elliot, Rod. A Beginner’s Guide to Potentiometers. Recovered [Online]

References II 8) Wagenaar, Daniel A. Potter, Steve M. A versatile all-channel stimulator for electrode arrays, with real-time control. Journal of Neural Engineering. Vol p ) Tehovnik, Edward J. Electrical stimulation of neural tissue to evoke behavioral responses. Journal of Neuroscience Methods. Vol p ) Cogan, Stuart F. Troyk, Philip R. Ehrlich, Julia. Plante, Timothy D. In Vitro Comparison of the Charge-Injection Limits of Activated Iridium Oxide (AIROF) and Platinum-Iridium Microelectrodes. IEE Transactions on Biomedical Engineering. Vol. 53, No. 9, September ) Ledwich, G [Online] Recovered February 20, DC/converter.shtm