Parametric Analysis of a Central Pttern Generator using Custom Analog Integrated CIrcuit Elements.

Using full custom analog integrated circuits, a comprehensive replica of the swim oscillator in Hirudo was created for the purposes of studying its operation, robustness, and stability as an oscillator. The neural element itself offers wide control over excitatory and inhibitory sensitivity, temporal characteristics, and input / output configuration, yet it is compact and efficient, with all critical internal nodes accessible. Based on neuronal connectivity as mapped out in published work, a cell-by-cell, synapse-by-synapse replica using eleven such cells was assembled on a printed circuit board, tuned to the characteristics and connectivities of each cell, and characterized for parametric sensitivity to a number of intracellular and extracellular factors such as ambient temperature and electrolyte levels. Cells were configured to replicate the behavior of the single-celled oscillators, reciprocally oscillatory pairs, and cyclically arranged ring oscillators documented in the Hirudo swim network present in each body segment. Robustness testing revealed that disabling of individual cells or small groups of cells did not disrupt the circuit’s rhythm. Parametric testing revealed that the embedded reciprocal and cyclic oscillator networks exhibited parametric sensitivities that sustained oscillatory rhythms even when multiple individual cells were eliminated. Tests also showed the reciprocal and cyclic multicellular networks showed parametric sensitivities that complemented one another, resulting in a network that held rhythm remarkably well over a broad range of inward and outward environmental conditions.