The generation of rhythmic activity dominates animal behaviour. Rhythmic activity plays important roles in the control of locomotion, breathing, feeding and circadian activity, and also in the control of various forms of cortical activity. Despite these diverse roles, common cellular principles underlie rhythm generation in invertebrate and vertebrate neuronal networks.

It can be demonstrated that rhythmic activity relies on a combination of intrinsic membrane properties, such as the activation of voltage-dependent calcium and sodium channels, and synaptic properties involving chemical and electrical transmission. These cellular properties are targets to neuromodulation, thus providing neural networks with the flexibility to respond to changes in the behavioural and environmental state of the animal.

This lecture will use the neural network that controls breathing in mammals as a model system to discuss general principles of rhythm generation. Our data indicate that the rhythm generating mechanisms in the respiratory network are state dependent. Under normoxic conditions, respiratory rhythm generation relies primarily on synaptic mechanisms. In contrast, during anoxia, the respiratory rhythm is primarily driven by pacemaker properties.

The transition from a primarily network-driven to primarily pacemaker-driven activity reflects two distinct forms of breathing: normal respiratory (eupnoeic) activity and gasping, respectively.