Transition to the UP state results in an increase in responsiveness in layer 5 neurons to synaptic inputs. A, Simultaneous extracellular multiple unit (MU) in layer 5 and intracellular recording from a layer 5 cell. The response of the cell to a single local electrical stimulus (Stim. location 2) was examined while the network was in the DOWN state (evoked PSP) or while it was in an UP state that had been triggered by a separate electrical stimulus (Stim. location 1) applied to the white matter (wm; evoked UP and PSP). B, Probability of initiation of a spike in response to the evoked PSPs during the UP and DOWN states. The UP state facilitates the probability of generating a spike to the smaller-amplitude inputs, whereas the large-amplitude synaptic responses initiate spikes with a high probability in both the DOWN and UP states. C, The UP state is associated with a decrease in the both the latency and jitter (SD of latency) of spikes that are initiated by the PSPs. Error bars indicate SEM; no bars indicates that they were smaller than the size of the symbol.