We experimentally study the collective activities in a developing clusterized rat cortical neuronal network in vitro monitored by a fluorescent calcium ion indicator. From the 7th day in vitro (DIV), the cultured neuronal network under the confluent condition (∼ 5000 cells/mm2) exhibits spontaneous firing of calcium spikes (each spike corresponds to a burst of action potential firing spikes) synchronized from the single neuron to the inter-cluster level, under the depletion of Mg2+. During the maturation process, not only the mean synchronous firing rate increases, but also the slow time scale dynamics emerges, i.e., the transition to the state of calcium bursts separated by quiescent periods. The bursting activities, e.g., the height of the leading spike in a burst and the burst width, are positively correlated to the length of the long quiescent period before but not after the burst. The memory of firing activities in a burst is not carried to the next quiescence and burst cycle. The ending of a burst is not due to the gradual decreasing number of neurons participating in the firing activity. The slow modulation can be tuned by changing the pharmacological condition. The removal of the slow modulation is always associated with the decrease of the calcium spike frequency. Possible mechanisms for slow modulation are discussed.
|Number of pages||12|
|Journal||Chinese Journal of Physics|
|State||Published - Apr 2008|