Abstracts

Low frequency ([lt]100Hz), low amplitude ([lt]100mV/mm) non-pulsatile electric fields have been shown to modulate epileptiform activity both in vitro and in vivo. The use of such subthreshold modulatory fields enables simultaneous stimulation and measurement, and allows continuous feedback control. Because of their inherent large low frequency common mode signal, off-the-shelf amplifiers for recording are not appropriate for this application. Therefore, we designed suitable hardware [ndash] electronics for recording, stimulation, and electrodes [ndash] for chronic applications. We have designed and implemented a complete stimulation and recording system, which includes headstages, isolated stimulators, and custom made software for continuous recording and simultaneous stimulation. The headstage preamplifiers are micro-powered (total consumption of 15mW), and can be connected to up to eight electrodes (four differential channels), and contain a MEMS-based biaxial DC accelerometer. Stimulation electronics are optically isolated from the recording system, and powered by two AA batteries for up to two weeks at a time. Both stimulation and recording are controlled by relatively low cost multifunction DAC cards in a standard PC. In performance tests, preamplifiers presented 4uV input referred noise. The frequency response (amplitude and phase) are shown in Figure 1A (upper curves). Depth electrode amplifiers were designed with a built-in lowpass filter. The system was tested in 6 chronically implanted animals (one week per animal), with reproducible and reliable results. Figure 1B shows typical examples of traces from the accelerometer, and EEG signals from two types of electrodes. We have demonstrated the performance and reliability of a recording and stimulation system designed for use with chronically implanted animals. This system is currently being used to assess the safety and efficacy of low frequency electrical stimulation, and will aid in the development of an adaptive epileptiform seizure control system.[figure1] (Supported by NIH grants R01EB001507, K02MH01493, and R01MH50006.)