Promising techniques to illuminate neuromodulatory control of the cerebral cortex in sleeping and waking states

•We review sleep/wake states of the cerebral cortex with a focus on neuromodulators.•Electrophysiological techniques have begun to decipher internal brain states.•Electrophysiology is unable to fully resolve the behavior of neuromodulators.•Fluorescence imaging is a prospective method useful in sleep research.