Low-cost acquisition of video images simultaneously with 240 electrophysiological signals

We developed a low-cost system for simultaneous collection and storage of physiological and video signals. The system samples and multiplexes up to 240 low-bandwidth analog channels with a camera video signal, and outputs a standard composite video signal containing analog and video data. The combined signals can be stored on video tape or can be digitized by an inexpensive framegrabber. The circuitry separates horizontal synchronizing pulses from a camera output; the pulses increment a counter that sequentially selects each electrophysiological channel on a sample-and-hold multiplexer. The intensity of each horizontal scan line from the multiplexer output represents the amplitude of one sample of each physiological channel. This signal is then multiplexed with the video signal, such that a portion of each video horizontal line represents the physiological data. The combined output is stored together, providing a means for synchronizing the two signals during analysis. The design allows easy coordination of electrophysiological events with video images from a standard video camera, avoiding the necessity for separate analog to digital circuitry for physiological and video signal storage on computer media, as well as the need for complex synchronization of the data from different media.