A Biophysically-Based Model of the Neostriatum as a Dynamically Reconfigurable Network

Physiological studies of the principal neurons of the neostriatum indicate that these cells have unusual membrane properties, which effectively give them two dynamically stable levels of membrane potential. One of these potential levels, the “up” state, allows the cell to fire in response to small changes in input spike frequency, while the other, the “down” state, leaves the cell relatively unresponsive and very resistant to firing. This chapter describes a biophysically-based model of this cell type, the medium spiny neuron, which demonstrates how the cell’s ion channels interact to produce this bistable response pattern. The model includes observed modulatory influences of dopamine and acetylcholine on these ion channels, which lead to the surprising property that the medium spiny cell can effectively act as a programmable binary latch. A network of these model cells can support proposed functions of the neostriatum, and predicts some of the symptoms of basal ganglia disorders such as parkinsonism.