Modeling network effects of dendritic plateau potentials in cortical pyramidal neurons

It has been demonstrated in brain slices that releasing glutamate near the basal dendrites of cortical pyramidal neurons can generate dendritic plateau potentials–-long-lasting depolarizations of the dendritic membrane mediated by activation of synaptic NMDA and AMPA receptors and extrasynaptic NMDA receptors. Depending on the location and strength of the glutamate stimulus, as well as on local dendritic morphology and activity, the depolarization from dendritic plateaus can spread into the soma, reducing membrane time constant and bringing the cell closer to the spiking threshold. Using data from voltage-sensitive dye imaging in dendrites and whole-cell patch measurements in somata of prefrontal cortex pyramidal neurons from rat brain slices, we developed a morphologically-detailed cortical pyramidal neuron model with active dendrites that reproduced experimental observations: a threshold for activation of the plateau, saturation of plateau amplitude but increasing plateau duration with increasing glutamate application, depolarization of the soma by approximately 20 mV, and back-propagating action potential amplitude attenuation and time delay. For use in network modeling, this cell model was then simplified morphologically while maintaining overall electrophysiological and plateau behavior. Network simulations demonstrated increased synchrony between cells during induced dendritic plateaus. These results support our hypothesis that dendritic plateaus provide a 200-500 ms time window during which a neuron is particularly excitable. At the network level, this predicts that sets of cells with simultaneous plateaus would provide an activated ensemble of responsive cells with increased firing. Synchronously spiking subsets of these cells would then create an embedded ensemble. This embedded ensemble would demonstrate a temporal code, at the same time as the activated (embedded) ensemble showed rate coding. This line of research may help to understand the implications of dendritic plateaus at the cellular and network level, and may lead to a better understanding of ensemble synchronization and multimodal cortical information processing.