Asymmetric Control of Coexisting Slow and Fast Rhythms in a Multifunctional Central Pattern Generator: A Model Study.

Using a simulation approach, we propose a biophysically feasible mechanism describing how a multifunctional central pattern generator (CPG) can produce co-existing slow and fast rhythms of the patterned motor output. This mechanism suggests that the same core elemental CPG can produce either a locomotion or a paw shaking rhythm in mammals (cat). We built a Hodgkin–Huxley-style biophysical model that generates multistability of a locomotion-like regime and a paw shake-like regime. This model is constructed as a half-center oscillator (HCO), in which two inhibitory neurons (representing the respective neuronal populations in real CPGs) reciprocally inhibit each other. We propose that the locomotion rhythm and the paw shaking rhythm are controlled by two different slowly inactivating intrinsic ion currents. In our model, slowly inactivating low voltage-activated calcium current (ICaS) drives the locomotion-like regime, while slowly inactivating sodium current (INaS) drives the paw shakelike regime. We investigated whether asymmetric characteristics of these regimes could be reliably and separately controlled by asymmetric variation of the conductances of these two currents. We found that variation of the conductance of ICaS in only one neuron, while holding this conductance constant in the other neuron, produces asymmetric changes in bursting characteristics, including the burst duration and interburst interval of the locomotion-like regime without producing notable changes of the paw shake-like regime. We also found that similar variation of the conductance of INaS affects the bursting characteristics of both regimes, although the paw shake-like regime is affected more remarkably than the locomotion-like one. [ABSTRACT FROM AUTHOR]