COORDINATION AND FREQUENCY CONTROLIN REDUCED MODELS OF LOCOMOTIONPATTERN GENERATING CIRCUITS

[摘要] The spinal hindlimb central pattern generators (CPGs) are capable of coordinating the hindlimbs in order to generate rhythmic activity in the absence of afferent feedback or rhythmic inputs. The excitability and adaptability of CPGs allow them to initiate, modify and maintain phase relationships between excitatory and inhibitory neuron groups. Many half-center CPG models of intricate symmetric units have been studied. However, a complete understanding of oscillatory mechanisms that operate locomotion activity is yet to be achieved. This study explores a simplified computational model of excitatory and inhibitory CPG units within different regimes of escape and release mechanisms. Our study shows that one model of a CPG network can operate in many different regimes and produce pertinent locomotor-like activity and phase relationships. Numerical simulations and phase-plane analysis were used to compare responses in oscillation frequency and phase duration to therange of values of excitatory or inhibitory external drive or the strength of synaptic inhibition to one or two half-centers of the cells that initiate the dynamics. Our analysis shows that oscillatory frequency and phase duration changes are highly dependent on the different intrinsic characteristics of the driving cells and the mechanisms of escape and release that prescribe transitions between active and silent phases of each cell within the network. In particular, intrinsic escape regimes displayed large ranges in phase duration control while intrinsic release models displayed the greatest degree of independence in the asymmetric case. Also, in the symmetric case, excitatory cells exhibited a larger range of period activity with respect to the changes to the applied external drive throughout. These results are explained using geometric phase plane analysis of the dynamics from explored regimes.

[发布机构] the University of Pittsburgh