Robust circuit rhythms in small circuits arise from variable circuit components and mechanisms

Abstract

Small central pattern generating circuits found in invertebrates have significant advantages for the study of the circuit mechanisms that generate brain rhythms. Experimental and computational studies of small oscillatory circuits reveal that similar rhythms can arise from disparate mechanisms. Animal-to-animal variation in the properties of single neurons and synapses may underly robust circuit performance, and can be revealed by perturbations. Neuromodulation can produce altered circuit performance but also ensure reliable circuit function.

Figure 1

Circuit oscillations can arise either from a bursting pacemaker neuron (left) or from circuit interactions (right). In each panel the neurons are first shown independently, then coupled by inhibitory synaptic interactions, as shown.

Figure 2

Responses of circuits with variable parameters can be reliable to modest perturbations but reveal their underlying structure in response to an extreme perturbation. Ion channels are shown in red and blue and vary in number in the different circuit configurations. Synaptic strength is shown by the size of the symbols. Electrical coupling is shown with resistor symbols and the remaining synapses are inhibitory. The bottom neuron class in each circuit varies in number, as in Daur et al. [30**].

Figure 3

Degenerate mechanisms for controlling the transition of the hn neuron from firing with the slow set of neurons to firing with the fast set of neurons. Note that each of three different changes in circuit parameters can produce virtually identical circuit outcomes. Taken from Gutierrez et al. [68**].