The cerebral cortex can generate persistent activity within local as well as long range networks through recurrent excitatory pathways.

This recurrent excitation is controlled and molded by the activation of inhibitory networks.

During slow wave sleep, the cerebral cortex generates spontaneous periods of persistent activity that fail, owing to the strong influence of Ca2+ and Na+-activated K+ currents.  These currents are reduced during waking, and this allows for the maintained excitability of neurons during this state.

The ability of the cerebral cortex to generate rhythmic, recurrent activity allows it to also generate some forms of epileptic seizures.

We suggest that the generation of persistent activity and setting the state of the membrane potential of neurons in recurrent networks in the cortex are both highly involved in:

Short term memory, 
Receptive field analysis and plasticity, 
and neuropsychological phenomenon, such as visual afterimages and perhaps even hallucinations.