A Novel Charge Neutral, Programmable, Wireless Brain Stimulation System for Rat Experiments

Deep Brain Stimulation (DBS) of brain regions such as the Subthalamic nucleus (STN) or Globus pallidum internum (GPi) is a clinical therapy for treating the motor symptoms of Parkinson's disease for the last few decades in humans when the drug-induced fluctuations are seen. Still, the regions involved in Parkinson's disease are under constant investigation for better outcomes with respect to gait, and research is actively carried out in this area on various animal models, especially on rats. Stimulator circuits required for electrical excitation of the brain in rat models need to be smaller than the rat's body, lightweight, and tether-free such that behavior is not affected during the experimentation. Parameters such as pulse amplitude and frequency need to be programmable in real-time since the exact values are not known prior. The stimulator needs to maintain charge neutrality such that extra charge should not be injected into the brain, which may adversely affect the experimental outcome. In this work, a wireless biphasic pulse generator (weight: 9.89 g without battery, dimensions: 4.3 cm x 3.8 cm) is developed and deployed in an anesthetized rat for intracortical microstimulation of the motor cortex region. A Bluetooth low-energy module integrated with the system facilitates wireless communication. The onboard microcontroller's current DAC unit is programmed to generate sink currents (0-2.04 mA) in real time. The current mirrors used in the design enable simultaneous multi-output pulse generation. The switching logic in the final stage generates biphasic pulses required for brain stimulation that can guarantee charge neutrality as the same network is involved in generating cathodic and anodic pulses. Additionally, the discrete components are chosen so that the turnaround time is less than two weeks compared to ASIC-based approaches, which typically take several months for development and testing.