NOISE-INDUCED SPIRAL WAVES IN ASTROCYTE SYNCYTIA SHOW EVIDENCE OF SELF-ORGANIZED CRITICALITY

Long range (a few centimeters), long lived (many seconds), spiral chem ical waves of calcium ions (Ca2+) are observed in cultured networks of glial cells for normal concentrations of the neurotransmitter kainate . A new method for quantitatively measuring the spatiotemporal size of the waves is described. This measure results in a power law distribut ion of wave sizes, meaning that the process that creates the waves has no preferred spatial or temporal (size or lifetime) scale. This power law is one signature of self-organized critical phenomena, a class of behaviors found in many areas of science. The physiological results f or glial networks are fully supported by numerical simulations of a si mple network of noisy, communicating threshold elements. By contrast, waves observed in astrocytes cultured from human epileptic foci exhibi ted radically different behavior. The background random activity, or ' 'noise'', of the network is controlled by the kainate concentration. T he mean rate of wave nucleation is mediated by the network noise. Howe ver, the power law distribution is invariant, within our experimental precision, over the range of noise intensities tested. These observati ons indicate that spatially and temporally coherent Ca2+ waves, mediat ed by network noise may play and important role in generating correlat ed neural activity (waves) over long distances and times in the health y vertebrate central nervous system.