The "DOWN" state is associated with a slow afterhyperpolarization and a relative refractory period for generating persistent activity
Figure 9. Activation of persistent activity with the local application of a pulse of glutamate at varying times from a previous pulse of glutamate revealed a relative refractory period for the "UP" state (A). This refractory period lasts for approximately 5 seconds. B. In many cortical pyramidal cells, the "DOWN" state is associated with the generation of a slow afterhyperpolarization (AHP) (b1). This ahp reduces the excitability of the neuron and suppresses its response to the intracellular injection of a depolarizing current pulse (b2).