A novel central pattern generator model for gait movements of rat hindlimbs

Central pattern generators (CPGs) are neural circuits which are found in both invertebrates and vertebrates, and are capable of generating rhythmic patterns of neural activity without receiving any rhythmic input. The mechanism by which CPG controls alternating and turning movements in vertebrates has not yet been fully understood. In this paper, a new CPG model for rat hindlimbs is proposed to unravel the above mechanism based on recent physiological experimental results. The model is obtained by adding commissural interneurons (CINs, including V0, V3, and CINi populations) and chx10 Gi neurons into Deng's CPG model. Based on our proposed CPG model, different alternating gaits in the rat hindlimb model can be achieved by ablating different populations of commissural interneurons, which is consistent with physiological experimental findings. Then, turning movements are studied by applying unilateral excitatory and inhibitory stimuli to chx10 Gi neurons which are connected to the flexion side of the CPG with inhibitory synapses. It is found that unilateral activation leads to turning towards the same side, while unilateral inhibition results in turning towards the opposite side, which is also consistent with the results in physiological experiments. Finally, the ion-channel control mechanism of CPG burst rhythms is investigated, and it is found that the CPG burst rhythm is most sensitive to sodium ion channels, with a significantly greater impact than the influence of reciprocal inhibition on the rhythm. The proposed CPG model provides a new perspective for understanding motor neural mechanism of vertebrates, and also could be adopted in motion control of hindlimb robots.