Analog VLSI-spinal cord interface for motor control

Our present understanding of neural locomotor control systems is primarily based upon results from experimental studies and some mathematical models. A device that could provide real-time interaction between complex mathematical models and actual biological systems would be very beneficial. We present a novel neuromorphic analog VLSI-spinal cord interface system for a lower vertebrate, the lamprey. The lamprey spinal cord has a distributed motor pattern generator, which can be described as a chain of coupled unit pattern generators. Our CMOS aVLSI circuit is based on a mathematical network model of a spinal unit pattern generator. It can be interfaced in real-time with the isolated spinal cord of the lamprey in both an open loop and closed loop mode. `Fictive' locomotor rhythm can be induced in the isolated lamprey spinal cord by chemical stimulation. This rhythm can dynamically modulate the activity of the aVLSI circuit. In turn, the aVLSI circuit can entrain the spinal locomotor rhythm. Since the VLSI neural network circuit is well characterized and some parameters of the model are readily modifiable, this real-time interface with the spinal cord provides experimental neurophysiologists a novel tool for investigating the role of specific neural components in locomotor rhythm generation and control.