A combined computational and intracellular study of correlated synaptic bombardment in neocortical pyramidal neurons in vivo

Computational models and intracellular recordings were combined to characte rize synaptic bombardment in neocortical pyramidal neurons during active st ates in vivo. Application of tetrodotoxin revealed that synaptic activity a ccounts for up to 80% of the input conductance. These experiments were repl icated assuming that excitatory and inhibitory synapses release randomly at high rates (1-5 Hz). A significant correlation between synaptic events had to be introduced to account for the membrane potential fluctuations record ed experimentally. We conclude that pyramidal neurons in vivo experience hi gh-frequency synaptic events with a significant correlation. The consequenc es of this synaptic bombardment on cellular responsiveness are investigated in the companion paper. (C) 2000 Elsevier Science B.V. All rights reserved .