Synaptic background activity affects the dynamics of dendritic integration in model neocortical pyramidal neurons

Neocortical pyramidal neurons in vivo are subject to an intense synaptic background activity which may significantly impact on dendritic integration, but this aspect is largely unexplored. Here we use computational models of morphologically-reconstructed pyramidal neurons, in which synaptic background activity was simulated according to recent measurements in cat parietal cortex. We show that background activity markedly enhances voltage attenuation, which results in a relative electrotonic "isolation" of different dendritic segments. On the other hand, the active propagation of action potentials in dendrites is minimally affected. The consequence is that inputs are integrated locally and their impact on the soma is independent on their position in the dendritic tree. We conclude that background activity sets up a dynamics of dendritic integration which is radically different compared to quiescent states. (C) 2001 Elsevier Science B.V. All rights reserved.