The "UP" state of the slow oscillation is generated through the arrival of the barrages of EPSPs and IPSPs, while the "DOWN" state is mediated by the withdrawal of activity
Figure 8. Intracellular recording from a cortical pyramidal cell during the "UP" state of the slow oscillation reveals the arrival of barrages of PSPs. Depolarization and hyperpolarization of the cell to different membrane potentials reveals that these PSPs are both excitatory and inhibitory (A). Blocking GABAA-receptor mediated inhibition with the local application of bicuculline demonstrates that the inhibitory PSPs control the amplitude of the "UP" state of the slow oscillation (B).