Sensitivity analysis of a hybrid neural network for locomotor control in the lamprey

Neural circuitry within the spinal cord of the lamprey forms a central pattern generator (CPG) for locomotor control, which interacts with particular neurons in a reticulo-spino-reticular (RSR) loop. Some of the CPG neurons have pacemaker properties. We have used mathematical models to examine the role of N-methyl-D-aspartate (NMDA) and calcium dependent potassium (K_Ca channel currents in generating oscillatory outputs in: (1) a single neuron; (2) a hybrid neural network for the CPG with embedded pacemaker neurons; and (3) a reticular CPG network. Neurons were modeled as isopotential single compartment units with simplified biophysical properties. All three conditions showed a minimum and maximum NMDA and K_Ca, conductance values for which oscillations occurred. The pacemaker neurons played an important role in the control of the locomotor rhythm by affecting the burst generation and termination mechanisms. The range over which oscillations can be obtained by altering the pacemaker properties of the neurons is affected by the architecture of the network. The pacemaker properties can provide a mechanism for frequency control by the brain with or without affecting the drive to the motor output units