waking periods or REM sleep, neurons reside mostly at up-state membrane potentials consistent with enhanced sensory input and synaptic drive. In acute slices of prefrontal cortex, neurons usually do not display spontaneous oscillations of membrane potentials (termed bistability) or action potential firing although these patterns can be elicited under certain conditions. For example, acute slices from the ferret visual or prefrontal cortex showed spontaneous oscillations in membrane potential when the ionic composition of the bathing solution was modified to mimic that of brain cerebrospinal fluid (Sanchez-Vives and McCormick, 2000). In rodents, slices of prefrontal cortex that are maintained in organotypic cell culture develop spontaneous oscillations in membrane potential during the first 2 weeks that are maintained for the life of the culture (Seamans et al., 2003; Tu et al., 2007). Similar patterns of activity can be induced in acute rodent slices by supplementing the bathing solution with optimal concentrations of NMDA and dopamine (Tseng and O’Donnell, 2004). Up-states in organotypic PFC cultures can also be evoked by applying brief trains of electrical pulses through a stimulating electrode and are accompanied by robust action potential firing. Paired recordings of neurons in PFC cultures show that the initiation and termination of up-states
