BME 4900 Final Report - Biomedical Engineering - University of ...

BME 4900 FINAL REPORT 5Team 82 Project Design2.1 BackgroundThe saccade controller consists of several connected neuron groups that fire insynchrony, based on external feedback, to cause an eye movement. The device willconsist of separate printed circuit boards for each neuron, connected in the mannerpresented in Enderle and Zhou (2010).In all of the alternative designs that weredeveloped, the construction of the device and the modeled neural network remained thesame.The flexibility of design presented itself in the selection of neuron modelsavailable. The three alternative designs under consideration were based on the Harmon,Roy, and FitzHugh-Nagumo models. In considering which model to use, the concernwas with complexity, cost, and accuracy. Safety, environmental, and sustainability issuesdo not differ between models, and also are essentially nonexistent.In 1971, Guy Roy proposed a simple model to reproduce the electrical propertiesof an axonal membrane. The conductance of each is represented by a simple circuitinvolving transistors, resistors, capacitors, and operational amplifiers. The circuits areshown in Fig. 1.Potassium ConductanceSodium ConductanceC6811N9146.8µF2.2kC6815.4k741 7410.12µF56k 39k 326k3.3µF20.4k486k220k39k 0.39µF1.2k14.7k470k560 92.8k12.4k20k2.68k560Figure 1. The potassium and sodium conductance circuits from the Roy model are shown. Supplyvoltages are ± 15 Volts. The output is defined across the source and drain of the transistor ineach.