An analog VLSI model of central pattern generation in the medicinal leech

The design and construction of a working silicon model of the neural system responsible for swimming behaviors of the medicinal leech (Hirundo medicinalis) are presented. The silicon model spans three levels of organization in the leech nervous system (neuron, ganglion, system) and represents one of the first comprehensive models of leech swimming. The circuit employs biophysically motivated analog neural elements networked to form biologically plausible ganglia. These ganglia are coupled using known interganglionic connections. Though the model is highly simplified, the output of this circuit is similar to the observed activity of the leech swim central pattern generator. The model operates on the same time-scale as its biological counterpart and may provide an excellent framework with which to explore adaptive response related to locomotion in the leech and other simple invertebrate nervous systems