Models of neocortical pyramidal neurons in the presence of correlated synaptic background activity: high discharge variability, enhanced responsiveness and independence of input location.
Michael Rudolph and Alain Destexhe

Society for Neuroscience Abstracts 26: 1623, 2000.

We have investigated detailed biophysical models of morphologically-reconstructed neocortical pyramidal neurons in which synaptic background activity (SBA) was simulated according to recent measurements in cat parietal cortex in vivo. The effects of correlation in the synaptic background was studied. As we showed, correlated SBA has a significant impact on various cellular properties and dendritic integration. First, the presence of correlated SBA resulted in spontaneous discharge patterns characterized by a high variability which is quantified by a coefficient of variation (CV) around unity. We investigated how the CV is affected by various cellular and synaptical background properties, especially the balance of excitation and inhibition. Second, the responsiveness of the neuron to additional periodic excitatory stimuli was significantly enhanced by SBA, through mechanisms similar to stochastic resonance. The influence of various parameters affecting membrane excitability was investigated. Third, the effectiveness of excitatory synaptic inputs was computed in the presence of correlated SBA. The overall efficacy of excitatory inputs was remarkably independent of input location due to the active propagation of action potentials in the dendritic tree. On the other hand, SBA markedly enhances voltage attenuation, leading to a relative electrotonic isolation of different dendritic segments. We conclude that a correlated SBA accounts for very particular electrophysiological properties of pyramidal neurons and suggest predictions to test this model.

Supported by: MRC and NIH