Institute for Mathematics and Its Applications
Charles Wilson, Univ. of Tennessee, Memphis
The neostriatum is a major target of cortical efferent projections, and an important site for convergence of inputs from diverse cortical areas. The pattern of activity in the population of functionally related cortical neurons converging onto individual striatal neurons can be estimated from their membrane potential fluctuations. Likewise, the membrane potential fluctuations of corticostriatal neurons largely reflects the activity of excitatory and inhibitory intracortical circuits Comparison of the membrane potential fluctuations of striatal and cortical projection neurons revealed that these signals were statistically similar. In both cases, excitatory and inhibitory input occurred together in episodes lasting 100 ms or longer. The durations of the episodes and the periods of relative quiet between them were statistically independent, and there were no serial correlations between the durations of successive episodes of synaptic activity. The mean membrane potential during such episodes was subthreshold in both neuron types, with action potentials arising from noisy fluctuations superimposed on the episodes of firing. The episodic pattern of synaptic input led to temporal clustering of firing in both cell types, but firing within the episode was irregular. In both cell types, the maintenance of a subthreshold mean membrane potential during episodes of strong synaptic activation prevented the development of rhythmic firing. Membrane potential was maintained below spike threshold both by synaptic inhibition that is recruited during episodes of excitation, and by voltage dependent potassium channels that are activated by synaptic excitation.