Spontaneous and Evoked Oscillations in Cultured Mammalian Neuronal Networks
In monolayer networks derived from dissociated embryonic mouse spinal cord tissue and maintained in culture for up to 9 months, near-oscillatory activity states are common and represent the most reproducible of all network behaviors. The oscillations, which are normally coordinated among many of the electrodes, can be generated in all spontaneously active cultures. Extensive observations of self-organized oscillatory activity have demonstrated that such network states represent a generic feature of randomized networks in culture and suggest that possibly all neuronal networks may have a strong tendency to oscillate. Whereas oscillatory states in normal culture medium are highly transient, system disinhibition produced by blocking inhibitory glycine or GABAA receptors generates long-lasting oscillatory states that survive for hours with minimal changes in burst variables. Electrical stimulation at a single electrode can generate driven periodic states and repeated stimulus trains have been observed to induce episodes of coherent bursting lasting beyond the termination of the stimulus pattern. Such responses appear “epileptiform” and might be considered a cultured network parallel to electrical induction of an epileptic seizure in vivo. These experimental observations suggest that oscillation, and not quiescence, is a natural state of neural tissue and challenge theoretical efforts to focus on oscillations as the basic “engine” of spontaneous activity.