Irregular behaviour in an excitatory - inhibitory neural network
- Excitatory-inhibitory networks arise in many regions throughout the central nervous system and display complex spatio-temporal firing patterns. The neuronal activity patterns (of individual neurons and/or the whole network) are closely related to the functional status of the system. One example is the basal ganglia, a group of subcortical nuclei that play an important role in the generation of movement. Dysfunction of the basal ganglia is associated with movement disorders such as Parkinson's disease and Huntington's chorea. Numerous experiments have demonstrated that neurons within the basal ganglia display a variety of dynamic behaviors such as correlated oscillatory activity and irregular, uncorrelated spiking. Patterns of neuronal activity differ between normal and pathological states. Neither the origins of these firing patterns nor the mechanisms that underlie the patterns are well understood. I consider a biophysical model of excitatory-inhibitory network in the basal ganglia and explore how specific biophysical properties of the network contribute to the generation of each activity and transitions between them. I use geometric dynamical systems and singular perturbation methods to reduce the model systematically to a simpler set of equations, which is suitable for analysis. The analysis reveals a set of concrete conditions for the generation of each activity pattern, especially of irregular behavior. The results specify the dependence on the strengths of synaptic connections and the intrinsic firing properties of the cells in the irregular regime when applied to the subthalamopallidal network of the basal ganglia.